Early Church Father, Irenaeus (c. AD 120–202), served the Lord as bishop of Lyons. One of his greatest contributions to the Christian Faith was his apologetic engagement with Marcion and the Gnostics. [1] His detailed exposition of Gnosticism in book 1 of his Against Heresies is our greatest surviving description of this sect. Irenaeus’ method of attack was to use the full range of apostolic writings, standing firm on the words of Paul and John. He defended biblical monotheism and the Oneness of God as the First Cause, whereas Gnostics taught that there were other gods (or personified aeons) [2] and another pleroma (the abode where God dwells). [3] Irenaeus observes that the vital error in Gnostic thought is they look for types and images beyond God and wander away, “never being able to fix their minds on the one true God.” [4] Irenaeus, not in the most tactful manner, expresses how “stupid” and “foolish” such people are, allowing their “imaginations to range beyond God.” [5] B