Irenaues of Lyons (c. 130–202) was the greatest theologian to arise in the Church1 since the time of the apostles. His Against Heresies2 is a masterpiece of ancient Christian literature, written by one schooled by another who was trained by the apostle John; in this work, consequently, readers have access to the teaching of a spiritual grandson of the apostle John. This alone would make it enormously important, but even apart from that circumstance, Against Heresies is profoundly significant: