Marcus Grodi and Msgr. Jeffrey Steenson continue their study of Against Heresies by St. Irenaeus of Lyons by beginning Book 4 of one of the most famous and important works of early Christian literature.

Here, St. Irenaeus deals with the Marcionite heresy, which pitted the New Testament against the Old Testament, and Jesus against the traditional Jewish concept of God. Irenaeus defends the orthodox Christian teaching that Jesus Christ is co-eternal with the Father as the second person of the Trinity, and who became flesh and dwelt among us, as St. John testifies in his Gospel.