The first Christians had no doubts about how to determine which was the true Church and which doctrines the true teachings of Christ. The test was simple: Just trace the apostolic succession of the claimants.
Apostolic succession is the line of bishops stretching back to the apostles. All over the world, all Catholic bishops are part of a lineage that goes back to the time of the apostles, something that is impossible in Protestant denominations (most of which do not even claim to have bishops).
The role of apostolic succession in preserving true doctrine is illustrated in the Bible. To make sure that the apostles’ teachings would be passed down after the deaths of the apostles, Paul told Timothy, “[W]hat you have heard from me before many witnesses entrust to faithful men who will be able to teach others also” (2 Tim. 2:2). In this passage he refers to the first three generations of apostolic succession—his own generation, Timothy’s generation, and the generation Timothy will teach.
The Church Fathers, who were links in that chain of succession, regularly appealed to apostolic succession as a test for whether Catholics or heretics had correct doctrine. This was necessary because heretics simply put their own interpretations, even bizarre ones, on Scripture. Clearly, something other than Scripture had to be used as an ultimate test of doctrine in these cases.
Thus the early Church historian J. N. D. Kelly, a Protestant, writes, “[W]here in practice was [the] apostolic testimony or tradition to be found? . . . The most obvious answer was that the apostles had committed it orally to the Church, where it had been handed down from generation to generation. . . . Unlike the alleged secret tradition of the Gnostics, it was entirely public and open, having been entrusted by the apostles to their successors, and by these in turn to those who followed them, and was visible in the Church for all who cared to look for it” (Early Christian Doctrines, 37).
For the early Fathers, “the identity of the oral tradition with the original revelation is guaranteed by the unbroken succession of bishops in the great sees going back lineally to the apostles. . . . [A]n additional safeguard is supplied by the Holy Spirit, for the message committed was to the Church, and the Church is the home of the Spirit. Indeed, the Church’s bishops are . . . Spirit-endowed men who have been vouchsafed ‘an infallible charism of truth’” (ibid.).
Here are examples of what early Christian writers had to say on the subject of apostolic succession:
“Through countryside and city [the apostles] preached, and they appointed their earliest converts, testing them by the Spirit, to be the bishops and deacons of future believers. Nor was this a novelty, for bishops and deacons had been written about a long time earlier. . . . Our apostles knew through our Lord Jesus Christ that there would be strife for the office of bishop. For this reason, therefore, having received perfect foreknowledge, they appointed those who have already been mentioned and afterwards added the further provision that, if they should die, other approved men should succeed to their ministry” (Letter to the Corinthians 42:4–5, 44:1–3 [A.D. 80]).
“When I had come to Rome, I [visited] Anicetus, whose deacon was Eleutherus. And after Anicetus [died], Soter succeeded, and after him Eleutherus. In each succession and in each city there is a continuance of that which is proclaimed by the law, the prophets, and the Lord” (Memoirs, cited in Eusebius, Ecclesiastical History 4:22 [A.D. 180]).
“It is possible, then, for everyone in every church, who may wish to know the truth, to contemplate the tradition of the apostles which has been made known to us throughout the whole world. And we are in a position to enumerate those who were instituted bishops by the apostles and their successors down to our own times, men who neither knew nor taught anything like what these heretics rave about” (Against Heresies 3:3:1 [A.D. 189]).
“But since it would be too long to enumerate in such a volume as this the successions of all the churches, we shall confound all those who, in whatever manner, whether through self-satisfaction or vainglory, or through blindness and wicked opinion, assemble other than where it is proper, by pointing out here the successions of the bishops of the greatest and most ancient church known to all, founded and organized at Rome by the two most glorious apostles, Peter and Paul—that church which has the tradition and the faith with which comes down to us after having been announced to men by the apostles. For with this Church, because of its superior origin, all churches must agree, that is, all the faithful in the whole world. And it is in her that the faithful everywhere have maintained the apostolic tradition” (ibid., 3:3:2).
“Polycarp also was not only instructed by apostles, and conversed with many who had seen Christ, but was also, by apostles in Asia, appointed bishop of the church in Smyrna, whom I also saw in my early youth, for he tarried [on earth] a very long time, and, when a very old man, gloriously and most nobly suffering martyrdom, departed this life, having always taught the things which he had learned from the apostles, and which the Church has handed down, and which alone are true. To these things all the Asiatic churches testify, as do also those men who have succeeded Polycarp down to the present time” (ibid., 3:3:4).
“[I]t is incumbent to obey the presbyters who are in the Church—those who, as I have shown, possess the succession from the apostles; those who, together with the succession of the episcopate, have received the infallible charism of truth, according to the good pleasure of the Father. But [it is also incumbent] to hold in suspicion others who depart from the primitive succession, and assemble themselves together in any place whatsoever, either as heretics of perverse minds, or as schismatics puffed up and self-pleasing, or again as hypocrites, acting thus for the sake of lucre and vainglory. For all these have fallen from the truth” (ibid., 4:26:2).
“The true knowledge is the doctrine of the apostles, and the ancient organization of the Church throughout the whole world, and the manifestation of the body of Christ according to the succession of bishops, by which succession the bishops have handed down the Church which is found everywhere” (ibid., 4:33:8).
“[The apostles] founded churches in every city, from which all the other churches, one after another, derived the tradition of the faith, and the seeds of doctrine, and are every day deriving them, that they may become churches. Indeed, it is on this account only that they will be able to deem themselves apostolic, as being the offspring of apostolic churches. Every sort of thing must necessarily revert to its original for its classification. Therefore the churches, although they are so many and so great, comprise but the one primitive Church, [founded] by the apostles, from which they all [spring]. In this way, all are primitive, and all are apostolic, while they are all proved to be one in unity” (Demurrer Against the Heretics 20 [A.D. 200]).
“[W]hat it was which Christ revealed to them [the apostles] 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 . . . If then these things are so, it is in the same degree manifest that all doctrine which agrees with the apostolic churches—those molds and original sources of the faith must be reckoned for truth, as undoubtedly containing that which the churches received from the apostles, the apostles from Christ, [and] Christ from God. Whereas all doctrine must be prejudged as false which savors of contrariety to the truth of the churches and apostles of Christ and God. It remains, then, that we demonstrate whether this doctrine of ours, of which we have now given the rule, has its origin in the tradition of the apostles, and whether all other doctrines do not ipso facto proceed from falsehood” (ibid., 21).
“But if there be any [heresies] which are bold enough to plant [their origin] in the midst of the apostolic age, that they may thereby seem to have been handed down by the apostles, because they existed in the time of the apostles, we can say: Let them produce the original records of their churches; let them unfold the roll of their bishops, running down in due succession from the beginning in such a manner that [their first] bishop shall be able to show for his ordainer and predecessor some one of the apostles or of apostolic men—a man, moreover, who continued steadfast with the apostles. For this is the manner in which the apostolic churches transmit their registers: as the church of Smyrna, which records that Polycarp was placed therein by John; as also the church of Rome, which makes Clement to have been ordained in like manner by Peter” (ibid., 32).
“But should they even effect the contrivance [of composing a succession list for themselves], they will not advance a step. For their very doctrine, after comparison with that of the apostles [as contained in other churches], will declare, by its own diversity and contrariety, that it had for its author neither an apostle nor an apostolic man; because, as the apostles would never have taught things which were self-contradictory” (ibid.).
“Then let all the heresies, when challenged to these two tests by our apostolic Church, offer their proof of how they deem themselves to be apostolic. But in truth they neither are so, nor are they able to prove themselves to be what they are not. Nor are they admitted to peaceful relations and communion by such churches as are in any way connected with apostles, inasmuch as they are in no sense themselves apostolic because of their diversity as to the mysteries of the faith” (ibid.).
“[T]he Church is one, and as she is one, cannot be both within and without. For if she is with [the heretic] Novatian, she was not with [Pope] Cornelius. But if she was with Cornelius, who succeeded the bishop [of Rome], Fabian, by lawful ordination, and whom, beside the honor of the priesthood the Lord glorified also with martyrdom, Novatian is not in the Church; nor can he be reckoned as a bishop, who, succeeding to no one, and despising the evangelical and apostolic tradition, sprang from himself. For he who has not been ordained in the Church can neither have nor hold to the Church in any way” (Letters 69[75]:3 [A.D. 253]).
“[T]here are many other things which most properly can keep me in [the Catholic Church’s] bosom. The unanimity of peoples and nations keeps me here. Her authority, inaugurated in miracles, nourished by hope, augmented by love, and confirmed by her age, keeps me here. The succession of priests, from the very see of the apostle Peter, to whom the Lord, after his resurrection, gave the charge of feeding his sheep [John 21:15–17], up to the present episcopate, keeps me here” (Against the Letter of Mani Called “The Foundation” 4:5 [A.D. 397])