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 viva voce, as the phrase is, and subsequently by their epistles. (Tertullian. The Prescription against heresies, XXI)

And indeed Onesimus himself greatly commends your good order in God, that ye all live according to the truth, and that no sect has any dwelling–place among you. Nor indeed do ye hearken to any one rather than to Jesus Christ, the true Shepherd and Teacher. […] 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 ye must flee as ye would wild beasts. For they are ravening dogs, who bite secretly, against whom ye must be on your guard, inasmuch as they are men who can scarcely be cured. (Saint Ignatius of Antioch. Epistle to the Ephesians, ch. 6–7)

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 to the hostel of the diocesan Caritas of Rome, Stazione Termini, Rome, February 14, 2010)

In the light of the economy of salvation, the Church sees no conflict between proclaiming Christ and engaging in interreligious dialogue. Instead, she feels the need to link the two in the context of her mission ad gentes. These two elements must maintain both their intimate connection and their distinctiveness; therefore they should not be confused, manipulated or regarded as identical, as though they were interchangeable. […] Dialogue should be conducted and implemented with the conviction that the Church is the ordinary means of salvation and that she alone possesses the fullness of the means of salvation. (John Paul II. Encyclical Redemptoris missio, no. 55, July 12, 1990)

Such an exhortation seems to us to be of capital importance, for the presentation of the Gospel message is not an optional contribution for the Church. It is the duty incumbent on her by the command of the Lord Jesus, so that people can believe and be saved. This message is indeed necessary. It is unique. It cannot be replaced. It does not permit either indifference, syncretism or accommodation. (Paul VI. Apostolic exhortation Evangelii nuntiandi, no. 5, December 8, 1975)

The Church’s commitment to evangelization can never be lacking, since according to his own promise, the presence of the Lord Jesus in the power of the Holy Spirit will never be absent from her: ‘I am with you always, even until the end of the world’ (Mt 28:20). The relativism and irenicism prevalent today in the area of religion are not valid reasons for failing to respond to the difficult, but awe-inspiring commitment which belongs to the nature of the Church herself and is indeed the Church’s ‘primary task’ (Benedict XVI, Homily, 25 April 2005). (Congregation for the Doctrine of the Faith, Doctrinal note on some aspects of evangelization, December 3, 2007)

Concretely, one must never lose sight of the fact that the Church does not find the source of her faith and her constitutive structure in the principles of the social order of any historical period. While attentive to the world in which she lives and for whose salvation she labours, the Church is conscious of being the bearer of a higher fidelity to which she is bound. It is a question of a radical faithfulness to the Word of God which she has received from Christ who established her to last until the end of the ages. (Congregation for the Doctrine of the Faith. Concerning the reply on the Congregation for the Doctrine of the Faith on the teaching contained in the Apostolic letter Ordinatio Sacerdotalis, October 28, 1995)

The Church’s constant missionary proclamation is endangered today by relativistic theories which seek to justify religious pluralism, not only de facto but also de iure (or in principle). As a consequence, it is held that certain truths have been superseded; for example, the definitive and complete character of the revelation of Jesus Christ, the nature of Christian faith as compared with that of belief in other religions, the inspired nature of the books of Sacred Scripture, the personal unity between the Eternal Word and Jesus of Nazareth, the unity of the economy of the Incarnate Word and the Holy Spirit, the unicity and salvific universality of the mystery of Jesus Christ, the universal salvific mediation of the Church, the inseparability — while recognizing the distinction — of the kingdom of God, the kingdom of Christ, and the Church, and the subsistence of the one Church of Christ in the Catholic Church. […] On the basis of such presuppositions, which may evince different nuances, certain theological proposals are developed — at times presented as assertions, and at times as hypotheses — in which Christian revelation and the mystery of Jesus Christ and the Church lose their character of absolute truth and salvific universality, or at least shadows of doubt and uncertainty are cast upon them. (Congregation for the Doctrine of the Faith. Declaration Dominus Iesus, no. 4, August 6, 2000)

For a long time, the reason for evangelization has not been clear to many among the Catholic faithful. It is even stated that the claim to have received the gift of the fullness of God’s revelation masks an attitude of intolerance and a danger to peace. (Congregation for the Doctrine of the Faith. Doctrinal note on some aspects of evangelization, December 3, 2007)

In the formation of their consciences, the Christian faithful ought carefully to attend to the sacred and certain doctrine of the Church. For the Church is, by the will of Christ, the teacher of the truth. It is her duty to give utterance to, and authoritatively to teach, that truth which is Christ Himself, and also to declare and confirm by her authority those principles of the moral order which have their origins in human nature itself. […] The disciple is bound by a grave obligation toward Christ, his Master, ever more fully to understand the truth received from Him, faithfully to proclaim it, and vigorously to defend it. (Vatican Council II. Declaration Dignitatis humanae, no. 14, December7, 1965)

The Catholic Church is alone in keeping the true worship. This is the fount of truth, this the house of Faith, this the temple of God: if any man enter not here, or if any man go forth from it, he is a stranger to the hope of life and salvation. Let none delude himself with obstinate wrangling. For life and salvation are here concerned, which will be lost and entirely destroyed, unless their interests are carefully and assiduously kept in mind (Divin. Instit. IV, 30. 11–12). (Pius XI. Encyclical Mortalium animos, no. 11, January 6, 1928)

Further, the Church which, together with the apostolic duty of teaching, has received the command to guard the deposit of faith, has also, from divine Providence, the right and duty of proscribing ‘knowledge falsely so called’ (1Tim 6:20), ‘lest anyone be cheated by philosophy and vain deceit’ (cf. Col 2:8). (Denzinger–Hünermann 3018. Vatican Council I, Session III, Dogmatic constitution concerning the Catholic Faith, April 25, 1870)

With the admonition of the apostle that ‘there is one God, one faith, one baptism’ (Eph 4:5) may those fear who contrive the notion that the safe harbor of salvation is open to persons of any religion whatever. They should consider the testimony of Christ Himself that ‘those who are not with Christ are against Him,’ (Lk 11:23) and that they disperse unhappily who do not gather with Him. Therefore ‘without a doubt, they will perish forever, unless they hold the Catholic faith whole and inviolate’ (Symbols. Athanasius). (Gregory XVI. Encyclical Mirari vos, no. 9, August 15, 1832)

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. 11, January 6, 1928)

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)

But, God forbid that the sons of the Catholic Church ever in any way be hostile to those who are not joined with us in the same bonds of faith and love; but rather they should always be zealous to seek them out and aid them, whether poor, or sick, or afflicted with any other burdens, with all the offices of Christian charity; and they should especially endeavor to snatch them from the darkness of error in which they unhappily lie, and lead them back to Catholic truth and to the most loving Mother the Church, who never ceases to stretch out her maternal hands lovingly to them, and to call them back to her bosom so that, established and firm in faith, hope, and charity, and ‘being fruitful in every good work’ (Col 1,10), they may attain eternal salvation. (Denzinger-Hünermann 2867. Pius IX. Encyclical Quanto conficiamur moerore, no. 8, August 10, 1863)

In the Document, ecumenical dialogue takes on a specific characteristic; it becomes a ‘dialogue of conversion,’ and thus, in the words of Pope Paul VI, an authentic ‘dialogue of salvation’ (Ecclesiam Suam, 6 August 1964). Dialogue cannot take place merely on a horizontal level, being restricted to meetings, exchanges of points of view or even the sharing of gifts proper to each Community. It has also a primarily vertical thrust, directed towards the One who, as the Redeemer of the world and the Lord of history, is himself our Reconciliation. (John Paul II. Encyclical Ut unum sint, no. 35, May 25, 1995)

If such dialogue is to be truly constructive it must involve not just the mutual openness of the participants but also fidelity to the identity of the Catholic faith. Only in this way will it be able to lead towards the unity of all Christians in ‘one flock with one shepherd’ (Jn 10:16) and thus heal that wound which prevents the Catholic Church from fully realising her universality within history. (Congregation for the Doctrine of the Faith. Responses to some questions regarding certain aspects of the doctrine of the Church, June 29, 2007)

Therefore the whole and entire Catholic doctrine is to be presented and explained: by no means is it permitted to pass over in silence or to veil in ambiguous terms the Catholic truth. […] moreover because outside the truth no true union can ever be attained. (Congregation for the Doctrine of the Faith. Instruction Ecclesia Catholica, no. II, December 20, 1949)

But the danger remains. Indeed, the worker in the apostolate is under constant fire. The desire to come together as brothers must not lead to a watering down or whittling away of truth. Our dialogue must not weaken our attachment to our faith. Our apostolate must not make vague compromises concerning the principles which regulate and govern the profession of the Christian faith both in theory and in practice. An immoderate desire to make peace and sink differences at all costs (irenism and syncretism) is ultimately nothing more than skepticism about the power and content of the Word of God which we desire to preach. The effective apostle is the man who is completely faithful to Christ’s teaching. He alone can remain unaffected by the errors of the world around him, the man who lives his Christian life to the full. (Paul VI. Encyclical Ecclesiam suam, no. 88, August 6, 1964)

Here it is not a question of altering the deposit of faith, changing the meaning of dogmas, eliminating essential words from them, accommodating truth to the preferences of a particular age, or suppressing certain articles of the Creed under the false pretext that they are no longer understood today. The unity willed by God can be attained only by the adherence of all to the content of revealed faith in its entirety. In matters of faith, compromise is in contradiction with God who is Truth. In the Body of Christ, ‘the way, and the truth, and the life’ (Jn 14:6), who could consider legitimate a reconciliation brought about at the expense of the truth? […] A ‘being together’ which betrayed the truth would thus be opposed both to the nature of God who offers his communion and to the need for truth found in the depths of every human heart. (John Paul II. Encyclical Ut unum sint, no. 35, May 25, 1995)

But Catholic doctrine tells us that the primary duty of charity does not lie in the toleration of false ideas, however sincere they may be, nor in the theoretical or practical indifference towards the errors and vices in which we see our brethren plunged. […] If, as We desire with all Our heart, the highest possible peak of well being for society and its members is to be attained through fraternity or, as it is also called, universal solidarity, all minds must be united in the knowledge of Truth, all wills united in morality, and all hearts in the love of God and His Son Jesus Christ. (Pius X. Encyclical Notre charge apostolique, August 15, 1910)

Although We know that Catholic teachers generally avoid these errors, it is apparent, however, that some today, as in apostolic times, desirous of novelty […] are accordingly in danger of gradually departing from revealed truth and of drawing others along with them into error. Another danger is perceived which is all the more serious because it is more concealed beneath the mask of virtue. There are many who, deploring disagreement among men and intellectual confusion, through an imprudent zeal for souls, are urged by a great and ardent desire to do away with the barrier that divides good and honest men; these advocate an ‘eirenism’ according to which, by setting aside the questions which divide men, they aim not only at joining forces to repel the attacks of atheism, but also at reconciling things opposed to one another in the field of dogma. […] But some through enthusiasm for an imprudent ‘eirenism’ seem to consider as an obstacle to the restoration of fraternal union, things founded on the laws and principles given by Christ and likewise on institutions founded by Him, or which are the defense and support of the integrity of the faith, and the removal of which would bring about the union of all, but only to their destruction. (Pius XII. Encyclical Humani generis, no. 11–12, August 12, 1950)

Even on the plea of promoting unity it is not allowed to dissemble one single dogma; for, as the Patriarch of Alexandria warns us, ‘although the desire of peace is a noble and excellent thing, yet we must not for its sake neglect the virtue of loyalty in Christ’ (Ep. 61: ib., 325). […] The only successful method will be that which bases harmony and agreement among Christ’s faithful ones upon all the truths, and the whole of the truths, which God has revealed. (Pius XII. Encyclical Orientalis Ecclesiae, no. 1, April 9, 1944)

Finally, there have been some commentaries on the Letter Ordinatio Sacerdotalis which have suggested that the document constitutes an additional and inopportune obstacle on the already difficult path of ecumenism. In this regard, it should not be forgotten that according to both the letter and the spirit of the Second Vatican Council (cf. Unitatis Redintegratio, 11), the authentic ecumenical task, to which the Catholic Church is unequivocally and permanently committed, requires complete sincerity and clarity in the presentation of one’s own faith. Furthermore, it should be noted that the doctrine reaffirmed by the Letter Ordinatio Sacerdotalis cannot but further the pursuit of full communion with the Orthodox Churches which, in fidelity to Tradition, have maintained and continue to maintain the same teaching. The singular originality of the Church and of the priestly ministry within the Church requires a precise clarity of criteria. Concretely, one must never lose sight of the fact that the Church does not find the source of her faith and her constitutive structure in the principles of the social order of any historical period. While attentive to the world in which she lives and for whose salvation she labours, the Church is conscious of being the bearer of a higher fidelity to which she is bound. It is a question of a radical faithfulness to the Word of God which she has received from Christ who established her to last until the end of the ages. (Congregation for the Doctrine of the Faith. Concerning the reply on the Teaching contained in the Apostolic letter Ordinatio Sacerdotalis)

The way and method in which the Catholic faith is expressed should never become an obstacle to dialogue with our brethren. It is, of course, essential that the doctrine should be clearly presented in its entirety. Nothing is so foreign to the spirit of ecumenism as a false irenicism, in which the purity of Catholic doctrine suffers loss and its genuine and certain meaning is clouded. At the same time, the Catholic faith must be explained more profoundly and precisely, in such a way and in such terms as our separated brethren can also really understand. Moreover, in ecumenical dialogue, Catholic theologians standing fast by the teaching of the Church and investigating the divine mysteries with the separated brethren must proceed with love for the truth, with charity, and with humility. When comparing doctrines with one another, they should remember that in Catholic doctrine there exists a ‘hierarchy’ of truths, since they vary in their relation to the fundamental Christian faith. (Vatican Council II. Decree Unitatis redintegratio, no. 11, November 21, 1964)

We cannot, however, forget the transcendence of the Gospel in relation to all human cultures in which the Christian faith has the vocation to root itself and come to fruition according to all its potentialities. However great the respect should be for what is true and holy in the cultural heritage of a people, this attitude does not demand that one should lend an absolute character to this cultural heritage. No one can forget that, from the beginning, the Gospel was a ‘scandal for the Jews and foolishness for the pagans’ (1Cor 1:23). Inculturation which borrows the way of dialogue between religions cannot in any way pledge itself to syncretism. (International Theological Commission. Faith and inculturation, no. 14, December, 1988)

How so great a variety of opinions can make the way clear to effect the unity of the Church We know not; that unity can only arise from one teaching authority, one law of belief and one faith of Christians. But We do know that from this it is an easy step to the neglect of religion or indifferentism and to modernism, as they call it. Those, who are unhappily infected with these errors, hold that dogmatic truth is not absolute but relative, that is, it agrees with the varying necessities of time and place and with the varying tendencies of the mind, since it is not contained in immutable revelation, but is capable of being accommodated to human life. (Pius XI. Encyclical Mortalium animos, no. 15, January 6, 1928)

Obviously we cannot agree with these various forms of religion [Jewish, Moslem, and Afro–Asiatic], nor can we adopt an indifferent or uncritical attitude toward them on the assumption that they are all to be regarded as on an equal footing, and that there is no need for those who profess them to enquire whether or not God has Himself revealed definitively and infallibly how He wishes to be known, loved, and served. Indeed, honesty compels us to declare openly our conviction that the Christian religion is the one and only true religion, and it is our hope that it will be acknowledged as such by all who look for God and worship Him. (Paul VI. Encyclical Ecclesiam suam, no. 107, August 6, 1964)

As regards the manner and method of proceeding in this work, the Bishops themselves will make regulations as to what is to be done and what is to be avoided, and shall see that these are observed by all. They shall also be on guard lest, on the false pretext that more attention should be paid to the points on which we agree than to those on which we differ, a dangerous indifferentism be encouraged, especially among persons whose training in theology is not deep and whose practice of their faith is not very strong. For care must be taken lest, in the so–called ‘irenic’ spirit of today, through comparative study and the vain desire for a progressively closer mutual approach among the various professions of faith, Catholic doctrine either in its dogmas or in the truths which are connected with them be so conformed or in a way adapted to the doctrines of dissident sects, that the purity of Catholic doctrine be impaired, or its genuine and certain meaning be obscured. Also they must restrain that dangerous manner of speaking which generates false opinions and fallacious hopes incapable of realization; for example, to the effect that the teachings of the Encyclicals of the Roman Pontiffs on the return of dissidents to the Church, on the constitution of the Church, on the Mystical Body of Christ, should not be given too much importance seeing that they are not all matters of faith, or, what is worse, that in matters of dogma even the Catholic Church has not yet attained the fullness of Christ, but can still be perfected from outside. They shall take particular care and shall firmly insist that, in going over the history of the Reformation and the Reformers the defects of Catholics be not so exaggerated and the faults of the Reformers be so dissimulated, or that things which are rather accidental be not so emphasized, that what is most essential, namely the defection from the Catholic faith, be scarcely any longer seen or felt. Finally, they shall take precautions lest, through an excessive and false external activity, or through imprudence and an excited manner of proceeding, the end in view be rather harmed than served. Therefore the whole and entire Catholic doctrine is to be presented and explained: by no means is it permitted to pass over in silence or to veil in ambiguous terms the Catholic truth regarding the nature and way of justification, the constitution of the Church, the primacy of jurisdiction of the Roman Pontiff, and the only true union by the return of the dissidents to the one true Church of Christ. It should be made clear to them that, in returning to the Church, they will lose nothing of that good which by the grace of God has hitherto been implanted in them, but that it will rather be supplemented and completed by their return. However, one should not speak of this in such a way that they will imagine that in returning to the Church they are bringing to it something substantial which it has hitherto lacked. It will be necessary to say these things clearly and openly, first because it is the truth that they themselves are seeking, and moreover because outside the truth no true union can ever be attained. (Congregation for the Doctrine of the Faith. Instruction Ecclesia Catholica of the Holy Office, December 20, 1949)

We believe it our duty and office to cut and uproot the noxious weeds we perceive growing, so that they do not take root and spread damage in the field of the Lord. Certainly, ever since the origins of the early Church, due to the necessity that the faith of the elect be proven like gold in the fire, the Apostle, vessel of election, wished to warn the faithful that if someone arise, of those who alter and amend the Gospel of Christ, spreading false doctrines and betraying the depository of the faith, even if it was an angel who evangelized something other than he had, it would be necessary to anathemize him. (Pius IX. Apostolic letter Ad apostolicae sedis, August 22, 1851)

Then after fourteen years I again went up to Jerusalem with Barnabas, taking Titus along also […] and I presented to them the gospel that I preach to the Gentiles – but privately to those of repute – so that I might not be running, or have run, in vain. Moreover, not even Titus, who was with me, although he was a Greek, was compelled to be circumcised, but because of the false brothers secretly brought in, who slipped in to spy on our freedom that we have in Christ Jesus, that they might enslave us – to them we did not submit even for a moment, so that the truth of the gospel might remain intact for you. (Gal 2:1–5)

For some are firm in the faith; and so it is to be hoped that their communicating with unbelievers will lead to the conversion of the latter rather than to the aversion of the faithful from the faith. These are not to be forbidden to communicate with unbelievers who have not received the faith, such as pagans or Jews, especially if there be some urgent necessity for so doing. But in the case of simple people and those who are weak in the faith, whose perversion is to be feared as a probable result, they should be forbidden to communicate with unbelievers, and especially to be on very familiar terms with them, or to communicate with them without necessity. (Saint Thomas Aquinas. Summa Theologica II–II, q. 10, a. 9)

Anyone who is so ‘progressive’ as not to remain in the teaching of the Christ does not have God; whoever remains in the teaching has the Father and the Son. 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 9–11)

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’ (2 Jn 10). (Pius XI. Encyclical Mortalium animos, no. 9, January 6, 1928)

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. […] 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, The unity of the Catholic Church, II, 6)

Since therefore we have such proofs, it is not necessary to seek the truth among others which it is easy to obtain from the Church; since the apostles, like a rich man [depositing his money] in a bank, lodged in her hands most copiously all things pertaining to the truth: so that every man, whosoever will, can draw from her the water of life (Rev 22:17). For she is the entrance to life; all others are thieves and robbers. On this account we are bound to avoid them, but to make choice of the thing pertaining to the Church with the utmost diligence, and to lay hold of the Tradition of the Truth. For how stands the case? Suppose there arise a dispute relative to some important question among us, should we not have recourse to the most ancient Churches with which the apostles held constant intercourse, and learn from them what is certain and clear in regard to the present question? For how should it be if the apostles themselves had not left us writings? Would it not be necessary, [in that case,] to follow the course of the tradition which they handed down to those to whom they did commit the Churches? To which course many nations of those barbarians who believe in Christ do assent, having salvation written in their hearts by the Spirit, without paper or ink, and, carefully preserving the ancient tradition, believing in one God, the Creator of heaven and earth, and all things therein, by means of Christ Jesus, the Son of God. (Saint Irenaeus of Lyons. Against Heresies. Book 3, ch. 4, 1, 2)

This being the case, he is the true and genuine Catholic who loves the truth of God, who loves the Church, who loves the Body of Christ, who esteems divine religion and the Catholic Faith above every thing, above the authority, above the regard, above the genius, above the eloquence, above the philosophy, of every man whatsoever; who sets light by all of these, and continuing steadfast and established in the faith, resolves that he will believe that, and that only, which he is sure the Catholic Church has held universally and from ancient time; but that whatsoever new and unheard–of doctrine he shall find to have been furtively introduced by some one or another, besides that of all, or contrary to that of all the saints, this, he will understand, does not pertain to religion, but is permitted as a trial […]. (Saint Vincent of Lerins. Commonitory for the Antiquity and Universality of the Catholic Faith, ch. 20, no. 48)

Again, as all who offer themselves are received whatever may be their form of religion, they thereby teach the great error of this age – that a regard for religion should be held as an indifferent matter, and that all religions are alike. This manner of reasoning is calculated to bring about the ruin of all forms of religion, and especially of the Catholic religion, which, as it is the only one that is true, cannot, without great injustice, be regarded as merely equal to other religions. (Leo XIII. Encyclical Humanum genus, no. 6, April 20, 1884)

Therefore, dear ones, from those [heretics of] which we are speaking, flee from them as a deadly poison, condemn them, withdraw from them and, if adverted by you, they don’t wish to correct themselves, avoid conversation with them because as it is written. ‘…their talk will eat its way like gangrene’ (2Tim 2:17). (Leo I, the Great. Homily 96 against the heresy of Eutyches, 3)

It is impossible for the most true God, who is Truth Itself, the best, the wisest Provider, and the Rewarder of good men, to approve all sects who profess false teachings which are often inconsistent with one another and contradictory, and to confer eternal rewards on their members. […] By it we are taught, and by divine faith we hold one Lord, one faith, one baptism. […] This is why we profess that there is no salvation outside the Church. (Leo XII. Encyclical Ubi primum, no. 14 May 5, 1824)