Apologeticae sive Theologiae Fundamentalis, Tomus II (Pars Altera): Demonstratio Catholica

Some non-Catholics concede that the Church was instituted by Christ, but they affirm that the individual Christian societies are as many real manifestations, as it were, of one ideal Church, or as many forms, as it were, which are related to the true Church of Christ just as rays broken by a prism are related to undivided light.

Thus in Germany many followers of indifferentism (e. g. Martensen, Hase, Kahnis, Hölder) think that there are as many churches of Christ as there are different confessions. In England the Puseyites and Ritualists maintain that at least three communions, the Roman Catholic, the Greek Orthodox and the Anglican, are "sister churches" or branches of the great ecclesiastical tree (Branch-Churches). Hence they suppose that several bodies can with equal right be called churches of Christ.

These errors, already proscribed by the Syllabus of Pius IX¹ and by the encyclical of the Holy Office², Leo XIII again rejected in these words: "The Church of Christ is therefore unique: whoever go apart stray from the will and precept of Christ the Lord."³

It is proved by the testimony of Christ himself, of the apostles of Christ, and of Christian antiquity.

1. In explicit words Christ affirms that the Church is unique. For speaking of the institution of the Church, He says: "Upon this rock I will build my Church."¹ He says that He will build not several churches, but one Church of His upon one rock. Elsewhere, discoursing of the Church already built, He says: "And other sheep I have, which are not of this fold [scil. from the people and synagogue of the Jews]: them also [the Gentiles] I must bring, and they shall hear my voice, and there shall be one fold and one shepherd."² Therefore the faithful from Jews and Gentiles are to be gathered into one and the same Church under one shepherd. Moreover, Christ preaches the one kingdom of God, embracing the whole world and consequently excluding every partition and plurality.

2. In deeds Christ instituted only one Church, in that He set one and the same authority over the multitude of the faithful. And so it is, as abundantly appears from what has been demonstrated. For He chose the one college of apostles to teach, sanctify, and direct all the faithful, and He strictly commanded all the faithful to be subject to this one authority. Nay more, over the college of apostles itself and over the whole flock of the faithful He set one Peter, that he might be the foundation, the key-bearer, and the shepherd of the whole Church.³ Therefore, by the intention of Christ, the Church excludes plurality.

1. By the words of the apostle the Church is called "house of God"¹ or "temple of God"² by a singular name, besides which no other could be built, since it is built up out of all the faithful "upon the foundation of the apostles and prophets, Jesus Christ himself being the chief cornerstone."³ Likewise St. Paul calls the Church the bride of Christ⁴ and the (mystical) body of Christ.⁵ Christ, however, does not have many brides, nor many bodies. Indeed, the doctor of the Gentiles expressly intimates this as well by comparing all the faithful of Christ to one body, whose head is Christ.⁶

2. In the time of the apostles a single universal Church existed in fact. For the epistles of the apostles are either inscribed and sent to particular congregations, which nevertheless were joined with the other churches, or to all the faithful of the whole world. Likewise the council of the apostles gathered at Jerusalem about twenty years after the death of Christ binds all the faithful and prescribes the same laws to all.⁷ No trace, therefore, of a divided Church appears in the time of the apostles. From which we rightly conclude that Christ instituted only one Church.

1. In word, the writers of the first centuries extol the oneness of the Church to the highest degree. E.g. the Didache: "Remember, Lord, your Church … and gather her from the four winds, sanctified, into your kingdom, which you have prepared for her."¹ Clement of Alexandria: "Since God is one and the Lord is one, for this reason also that which is supremely venerable is praised, and from the fact that it is unique, as being an imitation of the principle, which is one. Into the lot of one nature, therefore, the Church is co-opted, which is one, which the heresies strive to cut into many."² Cyprian: "God is one, and Christ is one, and the Church is one, and the chair is one, founded upon Peter by the Lord's voice."³ Other Fathers proclaim the Church one mother⁴ one dove of Christ,⁵ one bride of Christ,⁶ one temple of God.⁷

2. In deed, the Christians of the earliest times truly acknowledge only one Church of Christ. Those dissenting from the union of the Catholic Church were never regarded as churches, but as sects outside the Church. Many were the sects, one the Church. Indeed, not even the sects themselves boasted that there were several churches of Christ, but each one of them maintained that it was the one Church of Christ.

Therefore, by the testimony of Christ Himself, of Christ's Apostles, and of Christian antiquity, it is established beyond all doubt that Christ instituted only a single Church. Whatever, then, the true Church of Christ may be, it is certain that it alone must derive its origin from Christ, and that apart from it no other church exists by divine right. Hence it is illegitimate to speak of "sister Churches," or simply of several churches which, although divided from one another, nevertheless all deserve the name of the Church of Christ.