Saint Irenaeus was one of the most important of the early Church Fathers. He had impeccable credentials; he was taught from his youth by Saint Polycarp who in turn was taught from his youth by Saint John the Apostle and Evangelist and recipient of the Apocalypse of Our Risen Lord Jesus Christ. His work has lasted and will continue to last. Its importance today cannot be overstated as the same heresies he warned of as the sign of the coming of the Antichrist are back in full force threatening the Church on all sides.

From Father Alban Butler:

Rev. Alban Butler (1711–73).  Volume VI: June.
The Lives of the Saints.  1866.
 
June 28
St. Irenæus, Bishop of Lyons, Martyr
 
           See Tillemont, t. 3; Ceillier, t. 2, p. 135; Orsi, t. 2; F. Colonia, Hist. Littéraire de la Ville de Lyon, Sæc. 3, p. 133, and Dom Massuit, in his edition of this father’s works.

A.D. 202.


THIS saint is himself our voucher that he was born near the times of Domitian, consequently not in the close, as Dupin conjectures, but in the beginning of Adrian’s reign, about the year 120. He was a Grecian, probably a native of Lesser Asia. His parents who were Christians, placed him under the care of the great St. Polycarp, bishop of Smyrna. It was in so holy a school, that he learned that sacred science which rendered him afterwards a great ornament of the Church in the days of her splendour, and the terror of her enemies. St. Polycarp cultivated his rising genius, and formed his mind to piety by precepts and example; and the zealous scholar was careful to reap all the advantages which were offered him by the happiness of such a master. Such was his veneration for his sanctity, that he observed every action and whatever he saw in that holy man, the better to copy his example, and learn his spirit. He listened to his instructions with an insatiable ardour, and so deeply did he engrave them in his heart, that the impressions remained most lively even to his old age, as he declares in his letter to Florinus, quoted by Eusebius. St. Jerom informs us, that St. Irenæus was also a scholar of Papias, another disciple of the apostles. In order to confute the heresies of that age which, in the three first centuries, were generally a confused medley drawn from the most extravagant systems of the heathens and their philosophers, joined with Christianity, this father studied diligently the mythology of the Pagans, and made himself acquainted with the most absurd conceits of their philosophers, by which means he was qualified to trace up every error to its source, and set it in its full light. On this account he is styled by Tertullian, 3 “The most diligent searcher of all doctrines.” St. Jerom often appeals to his authority. Eusebius commends his exactness. St. Epiphanius calls him “A most learned and eloquent man, endowed with all the gifts of the Holy Ghost.” Theodoret styles him, “The light of the western Gauls.”

click on the below links for Saint Irenaeus, Against Heresies

Saint Irenaeus, Against Heresies - Part 1 | Books I and II

Saint Irenaeus, Against Heresies - Part 2 | Books III and IV

Saint Irenaeus, Against Heresies - Part 3 | Book V