Heresy is the obstinate denial or obstinate doubt after the reception of baptism of some truth which is to be believed by divine and Catholic faith; apostasy is the total repudiation of the Christian faith; schism is the refusal of submission to the Supreme Pontiff or of communion with the members of the Church subject to him. (Code of Canon Law, Can. 751)

As Isidore says (Etym. viii, 3), schism takes its name ‘from being a scission of minds,’ and scission is opposed to unity. Wherefore the sin of schism is one that is directly and essentially opposed to unity. For in the moral, as in the physical order, the species is not constituted by that which is accidental. Now, in the moral order, the essential is that which is intended, and that which results beside the intention, is, as it were, accidental. Hence the sin of schism is, properly speaking, a special sin, for the reason that the schismatic intends to sever himself from that unity which is the effect of charity: because charity unites not only one person to another with the bond of spiritual love, but also the whole Church in unity of spirit. (Saint Thomas Aquinas. Summa Theologica, II-II, q. 39, a. 1)

The essence of schism consists in rebelliously disobeying the commandments: and I say ‘rebelliously’ since a schismatic both obstinately scorns the commandments of the Church, and refuses to submit to her judgment. But every sinner does not do this, wherefore not every sin is a schism. (Saint Thomas Aquinas. Summa Theologica, II-II, q. 39, a. 1, sol. 2)

Accordingly schismatics properly so called are those who, wilfully and intentionally separate themselves from the unity of the Church; for this is the chief unity, and the particular unity of several individuals among themselves is subordinate to the unity of the Church, even as the mutual adaptation of each member of a natural body is subordinate to the unity of the whole body. Now the unity of the Church consists in two things; namely, in the mutual connection or communion of the members of the Church, and again in the subordination of all the members of the Church to the one head, according to Colossians 2:18,19: ‘Puffed up by the sense of his flesh, and not holding the Head, from which the whole body, by joints and bands, being supplied with nourishment and compacted, groweth unto the increase of God.’ Now this Head is Christ Himself, Whose viceregent in the Church is the Sovereign Pontiff. Wherefore schismatics are those who refuse to submit to the Sovereign Pontiff, and to hold communion with those members of the Church who acknowledge his supremacy. (Saint Thomas Aquinas. Summa Theologica, II-II, q. 39, a. 1)

Heresy and schism are distinguished in respect of those things to which each is opposed essentially and directly. For heresy is essentially opposed to faith, while schism is essentially opposed to the unity of ecclesiastical charity. Wherefore just as faith and charity are different virtues, although whoever lacks faith lacks charity, so too schism and heresy are different vices, although whoever is a heretic is also a schismatic, but not conversely. This is what Jerome says in his commentary on the Epistle to the Galatians [In Ep. ad Tit. iii, 10]: ‘I consider the difference between schism and heresy to be that heresy holds false doctrine while schism severs a man from the Church’ Nevertheless, just as the loss of charity is the road to the loss of faith, according to 1Timothy 1:6: ‘From which things’, i.e. charity and the like, ‘some going astray, are turned aside into vain babbling, so too, schism is the road to heresy’. Wherefore Jerome adds (In Ep. ad Tit. iii, 10) that ‘at the outset it is possible, in a certain respect, to find a difference between schism and heresy: yet there is no schism that does not devise some heresy for itself, that it may appear to have had a reason for separating from the Church.’ (Saint Thomas Aquinas. Summa Theologica, II-II, q. 39, a. 1)

But heretics, in holding false opinions regarding God, do injury to the faith itself; while schismatics, on the other hand, in wicked separations break off from brotherly charity, although they may believe just what we believe. Wherefore neither do the heretics belong to the Church catholic, which loves God; nor do the schismatics form a part of the same, inasmuch as it loves the neighbor […] (Augustine of Hippo. Of Faith and the Creed, X)

From this it is easy to see that men can fall away from the unity of the Church by schism, as well as by heresy. ‘We think that this difference exists between heresy and schism’ (writes Saint Jerome): ‘heresy has no perfect dogmatic teaching, whereas schism, through some Episcopal dissent, also separates from the Church’ (In Epist. ad Titum, cap. iii., v. 10-11). In which judgment Saint John Chrysostom concurs: ‘I say and protest (he writes) that it is as wrong to divide the Church as to fall into heresy’ (Hom. xi., in Epist. ad Ephes., n. 5). Wherefore as no heresy can ever be justifiable, so in like manner there can be no justification for schism. ‘There is nothing more grievous than the sacrilege of schism, there can be no just necessity for destroying the unity of the Church’ (S. Augustine, Contra Epistolam Parmeniani, lib. ii., cap. ii., n. 25). (Leo XIII. Encyclical Satis cognitum, no. 24, June 29, 1896)

Heresies and schisms have no other origin than that obedience is refused to the priest of God, and that men lose sight of the fact that there is one judge in the place of Christ in this world. (Saint Cyprian of Carthage. Epistle XII to Cornelius, no. 5, quoted by Leo XIII in the Encyclical Satis cognitum, no. 15, June 19, 1896)

Between heresy and schism this must be observed: heresy perverts the dogma, while schism, through episcopal rebellion, separates from the Church. […] Nevertheless, there is no schism that does not invent a heresy along with it to justify its distancing from the church. (Saint Jerome. Commentaries on the Letter of Saint Paul to Titus, Book I, c. 3, no. 10 – PL 26:598)

Thus the Western and Latin ‘Filioque’ became, in the following centuries, an occasion for schism, already brought about by Focio (882) but consummated and extended throughout almost all of the Christian east by the year 1054. The Eastern churches, separated from Rome, today still profess, within their symbol of faith, ‘in the Holy Spirit that proceeds from the Father’ without mention of the ‘Filioque’, while in the West we expressly state that the Holy Spirit ‘proceeds from the Father and the Son.’ (John Paul II. General audience, no. 5, November 7, 1990)

The Latin tradition of the Creed confesses that the Spirit proceeds from the Father and the Son (filioque). the Council of Florence in 1438 explains: ‘The Holy Spirit is eternally from Father and Son; He has his nature and subsistence at once (simul) from the Father and the Son. He proceeds eternally from both as from one principle and through one spiration… And, since the Father has through generation given to the only-begotten Son everything that belongs to the Father, except being Father, the Son has also eternally from the Father, from whom he is eternally born, that the Holy Spirit proceeds from the Son’ (Council of Florence: DS 1300-1301). (Catechism of the Catholic Church, no. 246)

The affirmation of the filioque does not appear in the Creed confessed in 381 at Constantinople. But Pope Saint Leo I, following an ancient Latin and Alexandrian tradition, had already confessed it dogmatically in 447 even before Rome, in 451 at the Council of Chalcedon, came to recognize and receive the Symbol of 381. The use of this formula in the Creed was gradually admitted into the Latin liturgy (between the eighth and eleventh centuries). The introduction of the filioque into the Niceno-Constantinopolitan Creed by the Latin liturgy constitutes moreover, even today, a point of disagreement with the Orthodox Churches. (Catechism of the Catholic Church, no. 247)

At the outset the Eastern tradition expresses the Father’s character as first origin of the Spirit. By confessing the Spirit as he ‘who proceeds from the Father’, it affirms that he comes from the Father through the Son (AG 2). The Western tradition expresses first the consubstantial communion between Father and Son, by saying that the Spirit proceeds from the Father and the Son (filioque). It says this, ‘legitimately and with good reason’ (Council of Florence: DS 1302), for the eternal order of the divine persons in their consubstantial communion implies that the Father, as ‘the principle without principle’ (Council of Florence: DS 1331), is the first origin of the Spirit, but also that as Father of the only Son, he is, with the Son, the single principle from which the Holy Spirit proceeds (cf. Council of Lyons II: DS 850). This legitimate complementarity, provided it does not become rigid, does not affect the identity of faith in the reality of the same mystery confessed. (Catechism of the Catholic Church, no. 248)

So, also, at the present time some are described as dissolving Christ by diminishing His dignity so far as this lies in their power. In saying that the Holy Spirit does not proceed from the Son, they lessen His dignity, since He together with the Father is the Spirator of the Holy Spirit. (Saint Thomas Aquinas. Contra errores Graecorum, Part II, Proglogue)

It must be said that the Holy Ghost is from the Son. For if He were not from Him, He could in no wise be personally distinguished from Him; as appears from what has been said above (q. 28, a.3; q.30, a.2). For it cannot be said that the divine Persons are distinguished from each other in any absolute sense; for it would follow that there would not be one essence of the three persons: since everything that is spoken of God in an absolute sense, belongs to the unity of essence. Therefore it must be said that the divine persons are distinguished from each other only by the relations. Now the relations cannot distinguish the persons except forasmuch as they are opposite relations; which appears from the fact that the Father has two relations, by one of which He is related to the Son, and by the other to the Holy Ghost; but these are not opposite relations, and therefore they do not make two persons, but belong only to the one person of the Father. If therefore in the Son and the Holy Ghost there were two relations only, whereby each of them were related to the Father, these relations would not be opposite to each other, as neither would be the two relations whereby the Father is related to them. Hence, as the person of the Father is one, it would follow that the person of the Son and of the Holy Ghost would be one, having two relations opposed to the two relations of the Father. But this is heretical since it destroys the Faith in the Trinity. Therefore the Son and the Holy Ghost must be related to each other by opposite relations. (Saint Thomas Aquinas. Summa Theologica, I, q. 36, a.2 sol)

Now there cannot be in God any relations opposed to each other, except relations of origin, as proved above (q.28, a.44). And opposite relations of origin are to be understood as of a ‘principle’ and of what is ‘from the principle.’ Therefore we must conclude that it is necessary to say that either the Son is from the Holy Ghost; which no one says; or that the Holy Ghost is from the Son, as we confess. Furthermore, the order of the procession of each one agrees with this conclusion. For it was said above (a.27, a.2,4; q.28, a.4), that the Son proceeds by the way of the intellect as Word, and the Holy Ghost by way of the will as Love. Now love must proceed from a word. For we do not love anything unless we apprehend it by a mental conception. Hence also in this way it is manifest that the Holy Ghost proceeds from the Son. (Saint Thomas Aquinas. Summa Theologica, I, q. 36, a.2 sol)

We derive a knowledge of the same truth from the very order of nature itself. For we nowhere find that several things proceed from one without order except in those which differ only by their matter; as for instance one smith produces many knives distinct from each other materially, with no order to each other; whereas in things in which there is not only a material distinction we always find that some order exists in the multitude produced. Hence also in the order of creatures produced, the beauty of the divine wisdom is displayed. So if from the one Person of the Fathr, two persons proceed, the Son and the Holy Ghost, there must be some order between them. Nor can any other be assigned except the order of their nature, whereby one is from the other. Therefore it cannot be said that the Son and the Holy Ghost proceed from the Father in such a way as that neither of them proceeds from the other, unless we admit in them a material distinction; which is impossible. (Saint Thomas Aquinas. Summa Theologica, I, q. 36, a.2 sol)

Hence also the Greeks themselves recognize that the procession of the Holy Ghost has some order to the Son. For they grant that the Holy Ghost is the Spirit ‘of the Son’; and that He is from the Father ‘through the Son.’ Some of them are said also to concede that ‘He is from the Son’; or that ‘He flows from the Son,’ but not that He proceeds; which seems to come from ignorance or obstinacy. For a just consideration of the truth will convince anyone that the word procession is the one most commonly applied to all that denotes origin of any kind. For we use the term to describe any kind of origin; as when we say that a line proceeds from a point, a ray from the sun, a stream from a source, and likewise in everything else. Hence, granted that the Holy Ghost originates in any way from the Son, we can conclude that the Holy Ghost proceeds from the Son. (Saint Thomas Aquinas. Summa Theologica, I, q. 36, a.2 sol)

The Nestorians were the first to introduce the error that the Holy Ghost did not proceed from the Son, as appears in a Nestorian creed condemned in the council of Ephesus. This error was embraced by Theodoric the Nestorian […] (Saint Thomas Aquinas. Summa Theologica, I, q. 36, a.2 ad 3)

In every council of the Church a symbol of faith has been drawn up to meet some prevalent error condemned in the council at that time. Hence subsequent councils are not to be described as making a new symbol of faith; but what was implicitly contained in the first symbol was explained by some addition directed against rising heresies. Hence in the decision of the council of Chalcedon it is declared that those who were congregated together in the council of Constantinople, handed down the doctrine about the Holy Ghost, not implying that there was anything wanting in the doctrine of their predecessors who had gathered together at Nicaea, but explaining what those fathers had understood of the matter. Therefore, because at the time of the ancient councils the error of those who said that the Holy Ghost did not proceed from the Son had not arisen, it was not necessary to make any explicit declaration on that point; whereas, later on, when certain errors rose up, another council [Council of Rome, under Pope Damasus] assembled in the west, the matter was explicitly defined by the authority of the Roman Pontiff, by whose authority also the ancient councils were summoned and confirmed. Nevertheless the truth was contained implicitly in the belief that the Holy Ghost proceeds from the Father. (Saint Thomas Aquinas. Summa Theologica, I, q. 36, a.2)

Whenever one is said to act through another, this preposition ‘through’ points out, in what is covered by it, some cause or principle of that act. But since action is a mean between the agent and the thing done, sometimes that which is covered by the preposition ‘through’ is the cause of the action, as proceeding from the agent; and in that case it is the cause of why the agent acts, whether it be a final cause or a formal cause, whether it be effective or motive. It is a final cause when we say, for instance, that the artisan works through love of gain. It is a formal cause when we say that he works through his art. It is a motive cause when we say that he works through the command of another. Sometimes, however, that which is covered by this preposition ‘through’ is the cause of the action regarded as terminated in the thing done; as, for instance, when we say, the artisan acts through the mallet, for this does not mean that the mallet is the cause why the artisan acts, but that it is the cause why the thing made proceeds from the artisan, and that it has even this effect from the artisan. This is why it is sometimes said that this preposition ‘through’ sometimes denotes direct authority, as when we say, the king works through the bailiff; and sometimes indirect authority, as when we say, the bailiff works through the king. Therefore, because the Son receives from the Father that the Holy Ghost proceeds from Him, it can be said that the Father spirates the Holy Ghost through the Son, or that the Holy Ghost proceeds from the Father through the Son, which has the same meaning. (Saint Thomas Aquinas. Summa Theologica, I, q. 36, a.3 sol)

In every action two things are to be considered, the suppositum acting, and the power whereby it acts; as, for instance, fire heats through heat. So if we consider in the Father and the Son the power whereby they spirate the Holy Ghost, there is no mean, for this is one and the same power. But if we consider the persons themselves spirating, then, as the Holy Ghost proceeds both from the Father and from the Son, the Holy Ghost proceeds from the Father immediately, as from Him, and mediately, as from the Son; and thus He is said to proceed from the Father through the Son. So also did Abel proceed immediately from Adam, inasmuch as Adam was his father; and mediately, as Eve was his mother, who proceeded from Adam; although, indeed, this example of a material procession is inept to signify the immaterial procession of the divine persons. (Saint Thomas Aquinas. Summa Theologica, I, q. 36, a.3, ad 1)

The controversy [with the Greeks], however, comes from the profession of this article [of the faith]. But the profession of this article comes form the Latin Church of a triple cause, that is, from the truth of the faith, from the necessity of [protecting against] danger, and from the authority of the Church. The faith dictated this [article of the faith], and a dangerous necessity made it imminent to assure that it be not denied by anyone (as the Greeks who had fallen into this peril) and the authority of the Church is there too. And therefore it should have been expressed without hesitation.
The cause of the negation of this article [by the Greeks] comes from a triple cause, that is, through ignorance, through pride, and through obstination. From ignorance, because they neither understood Scripture, nor did they have congruent reason or clear revelation. From pride, for since they repute themselves smarter and were not called, they did not want to profess what was not invented by them. Through obstination [since] so that they not be convinced and seem to be moving irrationally, they invented for themselves reasons in opposition to truth; and thus they dared to defend their own opinion and to oppose the authority of the Roman Church; and therefore they are become heretics, because they deny the truth of the faith, and schismatics, because they have withdrawn from the unity of the Church. (Saint Bonaventure of Bagnoregio. Commentaries on the Sentences of Peter Lombard, Book 1, dist. 11, a. 1, q.1, concl. – Latin)

In denying, moreover, that there is one head of the Church, namely, the holy Roman Church, they clearly dissolve the unity of the Mystical Body; for there cannot be one body if there is not one head, nor one congregation if there is not one ruler. Hence, John 10:16 says: There will be one fold and one shepherd. (Saint Thomas Aquinas. Contra errores Graecorum, Part II, Prologue)

In denying purgatory they also lessen the power of this sacrament which is offered in the Church both for the living and for the dead; for if purgatory does not exist, it avails the dead nothing; it cannot profit them if they are in hell, where there is no redemption; nor can it do them any good if they are in heaven, where they are in no need of our prayers. (Saint Thomas Aquinas. Contra errores Graecorum, Part II, Prologue)

Neither living nor lifeless faith remains in a heretic who disbelieves one article of faith. The reason of this is that the species of every habit depends on the formal aspect of the object, without which the species of the habit cannot remain. Now the formal object of faith is the First Truth, as manifested in Holy Writ and the teaching of the Church, which proceeds from the First Truth. Consequently whoever does not adhere, as to an infallible and Divine rule, to the teaching of the Church, which proceeds from the First Truth manifested in Holy Writ, has not the habit of faith, but holds that which is of faith otherwise than by faith. Even so, it is evident that a man whose mind holds a conclusion without knowing how it is proved, has not scientific knowledge, but merely an opinion about it. Now it is manifest that he who adheres to the teaching of the Church, as to an infallible rule, assents to whatever the Church teaches; otherwise, if, of the things taught by the Church, he holds what he chooses to hold, and rejects what he chooses to reject, he no longer adheres to the teaching of the Church as to an infallible rule, but to his own will. Hence it is evident that a heretic who obstinately disbelieves one article of faith, is not prepared to follow the teaching of the Church in all things; but if he is not obstinate, he is no longer in heresy but only in error. Therefore it is clear that such a heretic with regard to one article has no faith in the other articles, but only a kind of opinion in accordance with his own will. (Saint Thomas Aquinas. Summa Theologica, II-II, q. 5, a. 3)

And with the same yearning Our soul goes out to those whom the foul breath of irreligion has not entirely corrupted, and who at least seek to have the true God, the Creator of Heaven and earth, as their Father. Let such as these take counsel with themselves, and realize that they can in no wise be counted among the children of God, unless they take Christ Jesus as their Brother, and at the same time the Church as their mother. (Leo XIII. Encyclical Satis cognitum, no. 16, June 29, 1896)

The spouse of Christ cannot be defiled; she is uncorrupted and chaste. She knows one home, with chaste modesty she guards the sanctity of one couch. She keeps us for God; she assigns the children whom she has created to the kingdom. Whoever is separated from the Church and is joined with an adulteress is separated from the promises of the Church, nor will he who has abandoned the Church arrive at the rewards of Christ. He is a stranger; he is profane; he is an enemy. He cannot have God as a father who does not have the Church as a mother. If whoever was outside the ark of Noah was able to escape, he too who is outside. the Church escapes. The Lord warns, saying: ‘He who is not with me is against me, and who does not gather with me, scatters.’ He who breaks the peace and concord of Christ acts against Christ; he who gathers somewhere outside the Church scatters the Church of Christ. (Saint Cyprian of Carthage. On the Unity of the Catholic Church, II, 6)

Congratulations are due, when such as these are separated from the Church, lest they prey upon the doves and sheep with their cruel and venomous contagion. Bitterness cannot cling and join with sweetness, darkness with light, rains with clear weather, fighting with peace, sterility with fecundity, drought with running waters, storm with calm. Let no one think that the good can depart from the Church; the wind does not ravage the wheat, nor does the storm overturn the tree strongly and solidly rooted; the light straws are tossed about by the tempest; the feeble trees are thrown down by the onrush of the whirlwind. The Apostle Paul execrates and strikes at these, when he says: ‘They have gone forth from us, but they were not of us. For if they had been of us, they would have continued with us.’ Hence heresies have both frequently arisen and are arising, while the perverse mind has no peace, while discordant perfidy does not maintain unity. (Saint Cyprian of Carthage. On the Unity of the Catholic Church, 9-10)

These pan-Christians who turn their minds to uniting the churches seem, indeed, to pursue the noblest of ideas in promoting charity among all Christians: nevertheless how does it happen that this charity tends to injure faith? Everyone knows that John himself, the Apostle of love, who seems to reveal in his Gospel the secrets of the Sacred Heart of Jesus, and who never ceased to impress on the memories of his followers the new commandment ‘Love one another,’ altogether forbade any intercourse with those who professed a mutilated and corrupt version of Christ’s teaching: ‘If any man come to you and bring not this doctrine, receive him not into the house nor say to him: God speed you’ (2Jn 10). For which reason, since charity is based on a complete and sincere faith, the disciples of Christ must be united principally by the bond of one faith. Who then can conceive a Christian Federation, the members of which retain each his own opinions and private judgment, even in matters which concern the object of faith, even though they be repugnant to the opinions of the rest? And in what manner, We ask, can men who follow contrary opinions, belong to one and the same Federation of the faithful? (Pius XI. Encyclical Mortalium animos, no. 10, January 6, 1928)

The union of Christians can only be promoted by promoting the return to the one true Church of Christ of those who are separated from it, for in the past they have unhappily left it. To the one true Church of Christ, we say, which is visible to all, and which is to remain, according to the will of its Author, exactly the same as He instituted it. (Pius XI. Encyclical Mortalium animos, no. 9, January 6, 1928)

With his strong insistence on adhering to the integrity of the faith, it is not to be wondered at that he [Saint Jerome ] attacked vehemently those who left the Church; he promptly regarded them as his own personal enemies. ‘To put it briefly,’ he says, ‘I have never spared heretics, and have always striven to regard the Church’s enemies as my own’ (S. Jerome, Dial. contra Pelagianos, Prol. 2). To Rufinus he writes: ‘There is one point in which I cannot agree with you: you ask me to spare heretics – or, in other words – not to prove myself a Catholic’ (Contra Ruf., 3, 43). Yet at the same time Jerome deplored the lamentable state of heretics, and adjured them to return to their sorrowing Mother, the one source of salvation; (In Mich., I:I0-IS) he prayed, too, with all earnestness for the conversion of those ‘who had quitted the Church and put away the Holy Spirit’s teaching to follow their own notions’ (In Is., 16:1-S). (Benedict XV. Encyclical Spiritus Paraclitus, no. 38, September 15, 1920)

If anyone comes to you and does not bring this doctrine, do not receive him in your house or even greet him; for whoever greets him shares in his evil works. (2 Jn 1:10-11)

I urge you, brothers, to watch out for those who create dissensions and obstacles, in opposition to the teaching that you learned; avoid them. For such people do not serve our Lord Christ but their own appetites, and by fair and flattering speech they deceive the hearts of the innocent. For while your obedience is known to all, so that I rejoice over you, I want you to be wise as to what is good, and simple as to what is evil. (Rom 16, 17-19)

And indeed Onesimus himself greatly commends your good order in God, that you all live according to the truth, and that no sect has any dwelling-place among you. Nor, indeed, do you hearken to any one rather than to Jesus Christ speaking in truth. For some are in the habit of carrying about the name [of Jesus Christ] in wicked guile, while yet they practise things unworthy of God, whom you must flee as you would wild beasts. For they are ravening dogs, who bite secretly, against whom you must be on your guard, inasmuch as they are men who can scarcely be cured. (Saint Ignatius of Antioch. Epistle to the Ephesians, 6-7)

Such a one is to be turned away from, and whoever has separated himself from the Church is to be shunned. Such a man is perverted and sins and is condemned by his very self. […] That man bears arms against the Church; he fights against God’s plan. An enemy of the altar, a rebel against the sacrifice of Christ, for the faith faithless, for religion sacrilegious, a disobedient servant, an impious son, a hostile brother, despising the bishops and abandoning the priests of God, he dares to set up another altar, to compose another prayer with unauthorized words, to profane the truth of the Lord’s offering by false sacrifices, and not to know that he who struggles against God’s plan on account of his rash daring is punished by divine censure. […] (Saint Cyprian of Carthage. On the Unity of the Catholic Church, II, 6)

Since the Lord Jesus Christ sent the apostles to preach, (our rule is) that no others ought to be received as preachers than those whom Christ appointed; for ‘no man knows the Father save the Son, and he to whomsoever the Son will reveal Him’ (Mt 11:27). Nor does the Son seem to have revealed Him to any other than the apostles, whom He sent forth to preach– that, of course, which He revealed to them. Now, what that was which they preached– in other words, what it was which Christ revealed to them – can, as I must here likewise prescribe, properly be proved in no other way than by those very churches which the apostles founded in person, by declaring the gospel to them directly themselves, both vivâ voce, as the phrase is, and subsequently by their epistles. (Tertullian. The Prescription against heresies, XXI)

The proper purpose of this missionary activity is evangelization, and the planting of the Church among those peoples and groups where it has not yet taken root. Thus from the seed which is the word of God, particular autonomous churches should be sufficiently established and should grow up all over the world, endowed with their own maturity and vital forces. Under a hierarchy of their own, together with the faithful people, and adequately fitted out with requisites for living a full Christian life, they should make their contribution to the good of the whole Church. (Vatican Council II. Decree Ad gentes, no. 6, December 7, 1965)

For since they hold it for certain that men destitute of all religious sense are very rarely to be found, they seem to have founded on that belief a hope that the nations, although they differ among themselves in certain religious matters, will without much difficulty come to agree as brethren in professing certain doctrines, which form as it were a common basis of the spiritual life. […] Certainly such attempts can nowise be approved by Catholics, founded as they are on that false opinion which considers all religions to be more or less good and praiseworthy, since they all in different ways manifest and signify that sense which is inborn in us all, and by which we are led to God and to the obedient acknowledgment of His rule. Not only are those who hold this opinion in error and deceived, but also in distorting the idea of true religion they reject it, and little by little. turn aside to naturalism and atheism, as it is called; from which it clearly follows that one who supports those who hold these theories and attempt to realize them, is altogether abandoning the divinely revealed religion. (Pius XI. Encyclical Mortalium animos, no. 2-3, January 6, 1928)

The witness of charity, practised here in a special way, is part of the Church’s mission, together with the proclamation of the truth of the Gospel. (Benedict XVI. Address for the visit to the hostel of Caritas in the Termini station of Rome, February 14, 2010)

If he refuses to listen to them, tell the church. If he refuses to listen even to the church, then treat him as you would a Gentile or a tax collector. (Mt 18:17)

Children, it is the last hour; and just as you heard that the antichrist was coming, so now many antichrists have appeared. Thus we know this is the last hour. They went out from us, but they were not really of our number; if they had been, they would have remained with us. Their desertion shows that none of them was of our number. But you have the anointing that comes from the holy one, and you all have knowledge. I write to you not because you do not know the truth but because you do, and because every lie is alien to the truth. (1Jn 2:18-21)

Children, let no one deceive you. The person who acts in righteousness is righteous, just as he is righteous. Whoever sins belongs to the devil, because the devil has sinned from the beginning. Indeed, the Son of God was revealed to destroy the works of the devil. (1Jn 3: 7-8)

As we have said before, and now I say again, if anyone preaches to you a gospel other than the one that you received, let that one be accursed! Am I now currying favor with human beings or God? Or am I seeking to please people? If I were still trying to please people, I would not be a slave of Christ. (Gal 1:9-10)