St. Irenaeus, who was born around 125 AD, lived early enough in Church history to be only one generation removed from the Apostles. One of the major influential figures of his youth was St. Polycarp of Smyrna, who had known and learned from the Apostle John. That proximity to the people who actually knew Jesus had a great influence on Irenaeus’ later life and theology.

The second century was a time of controversy for the early Church, and Irenaeus was very involved in defending the teachings of the Apostles from some of the better-known heresies of the time. Montanism, which was a movement seeking to restore the proper use of the gifts of the Spirit — spoken of by St. Paul — as well as a stricter asceticism than was required by the universal Church, eventually died out in the third century. But a more serious heresy, that of Gnosticism, was the focus of much of Irenaeus’ writings, teaching, and energy.

The Gnostics believed, in direct contrast to the Scripture and the teachings of the Apostles, that the physical world was “evil” and not really part of God’s original plan. They maintained that they, and they alone, were possessed of a more enlightened or “secret” knowledge than other Christians — hence the term Gnostic, which is derived from the Greek word, gnosis, which means knowledge. Most pernicious of all was their belief that Christ was not truly human and that redemption was not freedom from sin but merely a release from an evil physical world.

Happily for the Church, there arose, at the same time, an ardent defender of the teachings of the Apostles. Irenaeus, who was likely born somewhere in Asia minor, became a priest sometime during the 170s; he served in the Province of Lyons. He became the second bishop of that city when its first prelate, St. Pothinus, was martyred in 177. As the head of the church in that diocese, Irenaeus lost no time in confronting the Gnostic heresy head-on.

In order to refute Gnosticism, Irenaeus composed a five-volume work entitled “Against Heresies,” considered today to be one of the first works of systematic theology. In it, he stressed the full humanity of Jesus and definitively showed that Gnostic beliefs were in direct opposition to both the Sacred Scripture and the teachings of the Apostles. His teaching turned the tide against the Gnostics and expedited the compilation of the Church’s list of authorized inspired writing (the “canon” of the Bible) as well as those creeds and teachings which represented the authentic faith of the Church.

The exact date and circumstances of Irenaeus’ death are not certain; he may have been martyred around the year 202 AD, but his continuing influence on the Church remains. In addition to his work “Against Heresies,” other fragments of his work have been compiled and translated and are still studied today.

In 2022, to recognize his significance, Pope Francis named Irenaeus a Doctor of the Church. His feast is June 28.

Sources for this article include:

catholicnewsagency.com/saint/st-irenaeus-285

franciscanmedia.org/saint-of-the-day/saint-irenaeus

Poncelet, Albert. “St. Irenaeus.” The Catholic Encyclopedia. Vol. 8. New York: Robert Appleton Company, 1910.

Schreck, Alan. “Catholic Church History from A to Z.” Michigan: Servant Publications, 2002.