POPE FRANCIS has announced that he is to declare St Irenaeus of Lyons (c.120-200) a Doctor of the Church, a Doctor of Unity. Irenaeus links us to the Apostolic Age; he claims to have known the martyr Polycarp, a disciple of the Apostle John. My final year at Cambridge was devoted to writing an undergraduate dissertation of 10,000 words on Irenaeus’s theology of grace. I remember vividly the aromatic smell of the wood in Girton College library as I laboured away with the Ante-Nicene Christian Fathers’ Irenaeus Against Heresies — and the terror that almost overcame me when I had to defend my work in a viva.

Discovering Irenaeus saved me from a peculiarly crippling strand of public-school religion which I encountered in Cambridge. The Cambridge Inter-Collegiate Christian Union (CICCU) was not Gnostic, of course, but it assumed a similar rigid division between the saved and the unsaved. There was also just a hint of that worrying Christian sadism so well described by Andrew Graystone in his recent Bleeding for Jesus (Books, 1 October; Podcast, 8 October).

I certainly got the impression from CICCU that our salvation was God’s plan B, to rescue a few of us out of the many. It was dependent on penal substitution: Christ being punished in our place. Irenaeus simply taught me to think of God differently. For him, creation was a pure gift. Christ’s coming was always part of the plan, the means by which God brought creation to fulfilment. The fall was unfortunate, but not a tragedy, merely a reflection of Adam and Eve’s immaturity. The incarnation healed us by reworking our human nature from the inside.

It is difficult to explain quite why this ancient Christian teaching liberated me, but I suppose at the heart of it was a conviction that, in spite of an early adult sense of lostness (which was what CICCU’s message appealed to), I belonged in my very being to God, as did everyone and everything else. The world, the universe, and the Church were fundamentally relational. Reality was not split into those who knew the truth and those who didn’t.

The Pope announced Irenaeus’s new status at a meeting of Roman Catholic and Orthodox scholars. As a Greek-speaking bishop, Irenaeus ministered in what is now south-central France. (He found the local language really difficult.) Against the Gnostics, Irenaeus believed that authentic Christianity was never sectarian. The Spirit works through tradition, not through private experiences, which are often divisive.

Today, when Gnosticism is rampant in the form of conspiracy theories, and when we obsess about personal authenticity while recklessly ruining the natural world, Irenaeus’s delight in the universality of the gospel and of God’s grace in and through all things is still the core of my Christian faith: “The glory of God is man fully alive, and the life of man is the vision of God.”