Among the sacramentals blessings occupy an important place. They include both praise of God for his works and gifts, and the Church’s intercession for men that they may be able to use God’s gifts according to the spirit of the Gospel. (Catechism of the Catholic Church, no. 1678)

This efficacy, where there is question of the eucharistic sacrifice and the sacraments, derives first of all and principally from the act itself (ex opere operato). […] if one refers to the ‘sacramentals’ and the other rites instituted by the hierarchy of the Church, then its effectiveness is due rather to the action of the Shurch (ex opere operantis Ecclesiae), inasmuch as She is holy and acts always in closest union with her Head. (Pius XII. Encyclical Mediator Dei, no. 27, November 20, 1947)

An apostate from the faith, a heretic, or a schismatic incurs a latae sententiae excommunication; […] An excommunicated person is forbidden: 1/ to have any ministerial participation in celebrating the sacrifice of the Eucharist or any other ceremonies of worship whatsoever; 2/ to celebrate the sacraments or sacramentals and to receive the sacraments; 3/ to exercise any ecclesiastical offices, ministries, or functions whatsoever or to place acts of governance. (Code of Canon Law, can. 1364 §1; can. 1331 §1)

In effect, those who have received the baptism of the heretics, having never been baptized before, should be confirmed only with an invocation of the Holy Spirit through the imposition of hands, since they have received merely the form of baptism without the strength of sanctification. […] The ablution should not be profaned with any repetition, but rather, as we have said, one should only invoke the sanctification of the Holy Spirit: so that that which no one receives from the heretics may be received from Catholic priests. (Denzinger-Hünermann 316. Leo I, the Great. Letter Regressus ad nos, c.7, March 21, 458)

The Holy Spirit works in the Church what the soul works in all the members of one body. […] It could happen that in a human body, or better, of a human body, a member has to be amputated: a hand, finger or foot. Does the soul by any chance go after the separated member? While it was attached the body, it lived; once amputated, it loses life. In the same way, someone is a Christian Catholic when he lives in the body; separated from it, he becomes a heretic, and the Spirit does not follow the amputated member. Therefore, if you wish to have life in the Holy Spirit, conserve charity, love truth, desire unity and you will reach eternity. (Saint Augustine of Hippo. Sermon 267, 4)

For when the Lord urged unanimity and peace upon His disciples, He said: ‘I say to you that if two of you agree upon earth concerning anything whatsoever that you shall ask, it shall be granted you by my Father who is in heaven. For wherever two or three have gathered together in my name, I am with them,’ showing that the most is granted not to the multitude but to the unanimity of those that pray. […] But how can he agree with anyone, who does not agree with the body of the Church herself and with the universal brotherhood? How can two or three be gathered in the name of Christ, who it is clear are separated from Christ and His gospel? For we did not withdraw from them, but they from us, and when thereafter heresies and schisms arose, […] The Lord, moreover, is speaking of His Church, and He is speaking to those who are in the Church, that if they are in agreement […]: ‘Where there are two or three, I am with them,’ He who established and made the Church did not separate men from the Church, but rebuking the faithless for their discord and commanding peace to the faithful by His word, He shows that He is with two or three who pray with one mind rather than with a great many who are in disagreement, and that more can be obtained by the harmonious prayer of a few than by the discordant supplication of many. (Saint Cyprian of Carthage. The unity of the Catholic Church, ch. XII)

And so, assenting entirely to the decrees of all the Pontiffs, our predecessors, in this case, and confirming them most fully and, as it were, renewing them by Our authority, of Our own initiative and certain knowledge We pronounce and declare that ordinations enacted according to the Anglican rite have hitherto been and are invalid and entirely void. (Denzinger-Hünermann 3319. Leo XIII, Apostolic Letter Curae et caritatis, September 13, 1896)

But some are more easily deceived by the outward appearance of good when there is question of fostering unity among all Christians. Is it not right, it is often repeated, indeed, even consonant with duty, that all who invoke the name of Christ should abstain from mutual reproaches and at long last be united in mutual charity? […] These things and others that class of men who are known as pan-Christians continually repeat and amplify; and these men, so far from being quite few and scattered, have increased to the dimensions of an entire class, and have grouped themselves into widely spread societies, most of which are directed by non-Catholics, although they are imbued with varying doctrines concerning the things of faith. […] They add that the Church in itself, or of its nature, is divided into sections; that is to say, that it is made up of several churches or distinct communities, which still remain separate, and although having certain articles of doctrine in common, nevertheless disagree concerning the remainder; […] This being so, it is clear that the Apostolic See cannot on any terms take part in their assemblies, nor is it anyway lawful for Catholics either to support or to work for such enterprises; for if they do so they will be giving countenance to a false Christianity, quite alien to the one Church of Christ. (Pius XI. Encyclical Mortalium animos, no. 3.4.7.8, January 6, 1928)

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, […] 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.’ 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? For example, those who affirm, and those who deny that sacred Tradition is a true fount of divine Revelation; those who hold that an ecclesiastical hierarchy, made up of bishops, priests and ministers, has been divinely constituted, and those who assert that it has been brought in little by little in accordance with the conditions of the time; those who adore Christ really present in the Most Holy Eucharist through that marvelous conversion of the bread and wine, which is called transubstantiation, and those who affirm that Christ is present only by faith or by the signification and virtue of the Sacrament; those who in the Eucharist recognize the nature both of a sacrament and of a sacrifice, and those who say that it is nothing more than the memorial or commemoration of the Lord’s Supper; those who believe it to be good and useful to invoke by prayer the Saints reigning with Christ, especially Mary the Mother of God, and to venerate their images, and those who urge that such a veneration is not to be made use of, for it is contrary to the honor due to Jesus Christ. (Pius XI. Encyclical Mortalium animos, no. 9, January 6, 1928)

‘He shall redeem in peace my soul’. Against them that love not peace: ‘in peace He shall redeem my soul.’ ‘Because with those that hated peace I was peace-making.’ ‘He shall redeem in peace my soul, from those that draw near to me.’ For from those that are afar from me, it is an easy case: not so soon doth he deceive me that saith, Come, pray to an idol: he is very far from me. Art thou a Christian? A Christian, he saith. Out of a neighbouring place he is my adversary, he is at hand. ‘He shall redeem in peace my soul, from those that draw near to me: for in many things they were with me.’ Wherefore have I said, ‘draw near to me?’ Because ‘in many things they were with me.’ […] Baptism we had both of us, in that they were with me: the Gospel we both read, they were in that with me: the festivals of martyrs we celebrated, they were there with me: Easter’s solemnity we attended, they were there with me. But not entirely with me: in schism not with me, in heresy not with me. In many things with me, in few things not with me. But in these few things wherein not with me, there is no profit to them of the many things wherein they were with me. (Saint Augustine of Hippo. Exposition on Psalm 55(54), no. 18)

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)

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” (Tit 3, 11). […] 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. The unity of the Catholic Church, Ch. XII)

The Church forbids the faithful to communicate with those unbelievers who have forsaken the faith they once received, either by corrupting the faith, as heretics, or by entirely renouncing the faith, as apostates, because the Church pronounces sentence of excommunication on both. (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. (2Jn: 9-11)

If anyone according to the holy Fathers, harmoniously with us and likewise with the Faith, does not with mind and lips reject and anathematize all the most abominable heretics together with their impious writings even to one least portion, whom the holy Catholic and apostolic Church of God, that is, the holy and universal five Synods and likewise all the approved Fathers of the Church in harmony, rejects and anathematizes, we mean Sabellius, Arius, Eunomius, Macedonius, Apollinaris, Polemon, Eutyches, Dioscurus, Timothy Aelurus, Severus, Theodosius, Colluthus, Themistius, Paul of Samosata , Diodorus, Theodore, Nestorius, Theodulus the Persian, Origen, Didymus, Evagrius, and briefly all the remaining heretics, […] let such a person be condemned. (Denzinger-Hünermann 518-520. Lateran Synod, Against the Monothelites, October 31, 649)

Surely nothing should be preferable to a Catholic man than that schisms and dissensions among Christians be torn out by the roots and that all Christians be ‘careful to keep the unity of the Spirit in the bond of peace’ (Eph 4:3)… But, that the faithful of Christ and the clergy should pray for Christian unity under the leadership of heretics, and, what is worse, according to an intention, polluted and infected as much as possible with heresy, can in no way be tolerated. (Denzinger-Hünermann 2887. Congregation for the Doctrine of the Faith. Letter to the bishops of England, September 16, 1864)