St. Irenaeus is the most important theologian of the second century, laying the foundation for all future Christian thinkers. Irenaeus tells us that he had known Polycarp, who had himself known the apostles and been appointed by them as the bishop of the church of Smyrna. This direct contact with the immediate successors of the apostles was of importance for Irenaeus in his later defense of Christian practice and teaching.

The Demonstration of the Apostolic Preaching, newly translated here from the ancient Armenian version, presents the same vision with exceptional clarity and simplicity. Written at the end of the second century, it outlines Christian teaching in a non-polemical, non-apologetic manner. The second century was an age not unlike our own: drawing upon various elements from a plethora of religions, the Gnostics conjured up their own diverse gods.

In response to this, Irenaeus exhorts his readers to hold fast to Scripture, and simply to see what is.