Saint Irenaeus and the Formation of the New Testament Canon

In the late 2nd century, Irenaeus of Lyon combated Gnostic teachings that challenged early Christian orthodoxy. Gnosticism, blending Greek philosophy with Christianity, held that matter was evil and denied Jesus Christ's full humanity. Marcion of Sinope produced his own gospel around 130-140 AD, which Irenaeus refuted in his work 'Against Heresies' (c. 180-190 AD). Irenaeus established four criteria for canonicity: apostolic authorship, scriptural proof from Revelation (linking the four living creatures to the four Gospels), oral tradition and apostolic succession, and widespread usage across churches. He argued that the churches founded by the apostles held consistent testimony, contradicting Gnostic claims. Irenaeus quoted or alluded to nearly every New Testament book except III John, Jude, and Philemon, and used non-heretical sources like Clement and the Shepherd of Hermas. His arguments helped solidify the Christian canon, though a definitive list emerged later. The recognition of the New Testament's authority was present from Christianity's early centuries.