Irenaeus of Lyons was born around the year 130 at Smyrna, on the coast of Asia Minor in what is now Turkey, and the great gift of his boyhood was that he sat at the feet of an old man named Polycarp, the bishop of Smyrna, who had himself known the apostle John. Years later Irenaeus could still see it. I am able to describe the very place in which the blessed Polycarp sat as he discoursed, he wrote, his goings out and his comings in, the manner of his life, and the things he told of his conversations with John and with the others who had seen the Lord. That memory was the root of everything Irenaeus became, for it meant he held the faith not as a clever theory but as something handed to him, hand to hand, from the apostles themselves.

He carried that faith far to the west, to Lyons in Gaul, today in France, where he served as a presbyter in the same small, suffering church that gave the martyrs of the year 177, the church of the slave girl Blandina and the old bishop Pothinus. Irenaeus was away in Rome when the persecution struck, and when he returned he found his bishop dead and was made bishop in his place. He spent the rest of his life as a pastor on the frontier and as the church's clearest mind against a danger more subtle than persecution.

The danger was the Gnostics, teachers who claimed a secret knowledge handed down in private, who held that the world and the body were the botched work of a lesser god, and that salvation meant escaping matter for a realm of pure spirit. Against them Irenaeus wrote his great work, Against Heresies, and his answer was as simple as it was deep. There is no secret gospel, he said; the true faith is the one taught openly in the churches the apostles founded, the same in every place, passed down for all to hear. Creation is not a mistake but the good work of the one God. And that God did not despise our flesh but took it: the Word became what we are to make us what he is. He gathered the whole human story, from Adam onward, into himself and healed it, a teaching he called recapitulation. Against those who sneered at the body, Irenaeus proclaimed that God so loved this material, mortal flesh that he became it and would raise it, and he could put the whole glory of it in a single sentence. It is best known today in the modern paraphrase, often linked to the theologian Hans Urs von Balthasar, that the glory of God is a human being fully alive; what Irenaeus actually wrote is humbler and more searching: the glory of God is a living man, and the life of man consists in beholding God.

He died around the year 202. We do not know exactly how; a later tradition says he was martyred, though the earliest writers do not mention it. What we do know is the thing he gave the church, which was not a new idea but an old one kept safe: that the gospel is not a secret for the few but a gift handed openly to all, that the God who made the world is the God who saved it, and that a human being alive and beholding God is the very glory for which the world was made. The Gnostics promised escape from the flesh. Irenaeus promised its resurrection, and it is his hope, not theirs, that the church still holds.