Popular Patristics Series Volume 17 St. Irenaeus was, undisputedly, the most important theologian of the second century who laid a firmer foundation for all future Christian thinkers. Both in his work, Against the Heresies and in this present study, Demonstration of the Apostolic Preaching, St. Irenaeus explains that there is but one God, made known to the human race by his one Son, Jesus Christ, through...