Written in the late second century, Against Heresies is one of the most important works of early Christianity. Irenaeus, bishop of Lyons and a disciple of Polycarp (who himself had been taught by the Apostle John), stands as a living bridge between the Apostles and the generations that followed.

In this five-volume masterpiece, Irenaeus dismantles the false teachings of the Gnostics—those who claimed to possess “secret knowledge”—and boldly defends the faith “once for all delivered to the saints.” Along the way, he provides one of the earliest accounts of Apostolic succession, affirms the unity of Scripture, explains the goodness of creation, and proclaims the heart of the Gospel: the Word of God truly became flesh for our salvation.

More than a refutation, Against Heresies is a positive vision of the Church’s faith and mission. It is here that we first encounter the profound idea of Christ as the “new Adam” who recapitulates all things, restoring creation through His obedience and victory.
For anyone seeking to understand what the early Church believed, how it preserved the Apostolic tradition, and why those truths still matter today, Against Heresies is essential reading.