John Kaufman is Associate Professor of church history at MF Norwegian School of Theology, Religion and Society, Oslo. His primary research interest is in early Christian theology, in particular the second century. He wrote his dissertation on the doctrine of deification in Irenaeus. In addition to his dissertation, his article “Historical relativism and the essence of Christianity”, published in Studia Theologica (2016), is relevant to the topic of his chapter in this volume.