If theology is “thinking about faith” and arranging those thoughts in some systematic order, then Irenaeus has been rightly recognized by Catholics and Protestants alike as the first great systematic theologian.

There is considerable doubt about the year of Irenaeus’ birth; estimates vary from 97 to 160. It is certain that he learned the Christian faith in Ephesus at the feet of the venerable Polycarp, who in turn had known John the Evangelist. Some years before 177, probably while Irenaeus was still in his teens, he carried the tradition of Christianity to Lyons in southern France.