It is not right to say that [the apostles] preached before they had come to perfect knowledge, as some dare to say, boasting that they are the correctors of the apostles. For after our Lord had risen from the dead, and they were clothed with the power from on high when the Holy Spirit came upon them, they were filled with all things and had perfect knowledge. They went out to the ends of the earth, preaching the good things that come to us from God.

The tradition of the apostles can be clearly seen in every church by those who wish to behold the truth. We can enumerate those who were established by the apostles (and their successors) in the churches down to our time—none of whom taught or thought of anything like the heretics’ mad ideas. Even if the apostles had known of “hidden mysteries” (which they had taught to the “perfect” secretly and apart from others), they would have handed them down especially to those to whom they were entrusting the churches themselves. For they certainly wished those whom they were leaving as their successors to be perfect and irreproachable.

Apostolic Succession

[Take] the very great, oldest, and well-known church, founded and established at Rome by those two most glorious apostles Peter and Paul. When the blessed apostles had founded and built up the church, they handed over the episcopate to Linus. (Paul mentions this Linus in his epistles to Timothy.) Anencletus succeeded him. After him, Clement received the lot of the episcopate. He had seen the apostles and associated with them and still had their preaching sounding in his ears and their tradition before his eyes. (And not he alone, for there were many still left in his time who had been taught by the apostles.)

Similarly Polycarp, who not only was taught by apostles, and who associated with many who had seen Christ, was installed by apostles for Asia as bishop in the church in Smyrna. (I saw him myself in my early youth.) He survived for a long time and departed this life in a ripe old age by a glorious and magnificent martyrdom. He always taught what he learned from the apostles, which the church continues to hand on, and which are the only truths. The churches in Asia all bear witness to this, as do those who have succeeded Polycarp down to the present time. He is certainly a much more trustworthy and dependable witness than Valentinus and Marcion and the other false thinkers!

Since there are so many clear testimonies, we should not seek from others for the truth that can easily be received from the church. There the apostles, like a rich man making a deposit, fully bestowed upon her all that belongs to the truth, so that whoever wishes may receive from her the water of life. She is the entrance to life; all the others are thieves and robbers.

What if there should be a dispute about some matter of moderate importance? Should we not turn to the oldest churches, where the apostles themselves were known, and find out from them the clear and certain answer to the problem now being raised? Even if the apostles had not left their Writings to us, ought we not to follow the rule of the tradition that they handed down to those to whom they committed the churches?

Irenaus of Lyon (c.130–c.200)
Against the Heresies