The emergence of Christian theology and the beginning of European culture are closely entwined. Remove Christian ideas from Europe, and its philosophy, art, literature and music cannot be understood. Yet the emergence of Christian thought was precarious, ‘the nearest run thing you ever saw in your life’, and its survival has been through challenge and dispute.

Such challenge brings special times of movement in the history of ideas. Christian thought displayed fresh vigour in the second half of the second century. In contrast to the Apostolic Fathers, who were largely concerned with domestic affairs, Christian argument developed rapidly in the highly original writings of Justin, Athenagoras, Irenaeus, Clement of Alexandria and Tertullian. We witness an intellectual acceleration when, for the first time, there was a Christian Bible to expound and when New Testament ideas took off with such speed that the opposition became increasingly irrelevant. This is one of those brief periods of human invention when earlier concepts become museum pieces. Any such expansion requires at least four things: some thinkers to think, new resources to use, questions to answer, and an opposition to challenge.

The theologians who followed on from the writings which we call the New Testament were several and their contributions were of unequal worth.