Saint Irenaeus (born c. 120/140 in Asia Minor, died c. 200/203, probably in Lyon; Western feast day June 28; Eastern feast day August 23) was Bishop of Lugdunum (Lyon), apologist, and one of the leading Christian theologians of the 2nd century. His work Adversus haereses (Against Heresies), written c. 180, was a refutation of Gnosticism. In the course of his writings, Irenaeus contributed to the development of a canon of Scripture, the creed, and the authority of the episcopal office.
Early career
Although his exact date of birth is unknown, Irenaeus was born to Greek parents in Asia Minor. His own writings establish some biographical details, including that as a child he heard and saw Saint Polycarp, the last known link to the Apostles, in Smyrna, before that elderly Christian was martyred in 155. Eusebius of Caesarea also mentions that after the persecutions in Gaul in 177, Irenaeus succeeded the martyr Pothinus as bishop of Lugdunum. According to Eusebius, author of a fourth-century history of the Church, before becoming bishop, Irenaeus had been a missionary in southern Gaul and a peacemaker among the churches of Asia Minor troubled by heresy.
The known biographical data, combined with his published works, are sufficient to paint a portrait of a singular life. Historical sources attest to a close cultural connection between Asia Minor and southern France (the Rhone Valley) in the 2nd century. According to tradition, Saint John the Apostle, very old and having "seen the Lord" (i.e. Jesus), lived in Ephesus at the time when Polycarp was young. Thus, three generations separated Jesus of Nazareth from Irenaeus of southern France.
Mediations and Tensions in the Church
Irenaeus' time was marked by expansion and internal tensions within the Church. In many cases, Irenaeus acted as a mediator between different warring factions. The churches of Asia Minor always celebrated Easter on the same date (the 14th of Nisan) that the Jews celebrated Passover, while the Roman Church maintained that Easter should always be celebrated on a Sunday (the day of Christ's Resurrection). Mediating between the parties, Irenaeus argued that differences in external factors, such as the dates of festivals, should not be so severe as to destroy the unity of the Church.
Writings of Irenaeus: Conflict with the Gnostics
However, Irenaeus took a completely negative and unreactive attitude toward Marcion, a schismatic leader in Rome, and toward Gnosticism, a fashionable intellectual movement in the rapidly expanding Church that advocated dualism. Because Gnosticism was overcome by the early Church Fathers, including St. Clement of Alexandria and Irenaeus, the Gnostic writings were largely destroyed. In reconstructing Gnostic doctrines, modern scholars have therefore relied heavily on the writings of Irenaeus, who summarized Gnostic views before attacking them. After the discovery of the Gnostic library near Najʿ Ḥammādī (in Egypt) in the 1940s, respect for Irenaeus increased: he proved to be extremely accurate in his reporting of the doctrines he rejected. All of his known writings are devoted to the conflict with the Gnostics. His main work consists of five books in a work entitled Adversus haereses. Originally written in Greek around 180, Against Heresies is now known in its entirety only in a Latin translation, the date of which is disputed (200 or 400?). A shorter work by Irenaeus, The Manifestation of the Apostolic Preaching, also written in Greek, is extant only in an Armenian translation probably intended for the instruction of young candidates for baptism. Irenaeus positively affirmed the validity of the Hebrew Bible (the Christian Old Testament), which the Gnostics denied, claiming that it upheld the laws of the creator God of wrath. Although Irenaeus does not explicitly refer to two testaments, an old and a new, he prepared the ground for this terminology. He affirmed the validity of both testaments at a time when concern for the unity and difference between the two parts of the Bible was growing. Numerous works claiming scriptural authority, including many by the Gnostics, flourished in the second century. By attacking the Gnostics, Irenaeus helped to diminish the importance of these works and establish a canon of Scripture.
Establishment of the Scriptures and the Creed
The development of the creed and the office of bishop can also be traced to his conflicts with the Gnostics. Based solely on the New Testament, which concerns the salvation of humanity, one would not expect the creed to begin with an article on the creation of the world and humans. But because the Gnostics denied that the God revealed in the New Testament was the Creator, the first article of the creed was, for polemical reasons, directly linked to Genesis ("In the beginning God created the heavens and the earth"). Irenaeus refers to the creed as a "Rule of Truth" used to combat heresy. The earliest lists of bishops were also countermeasures against the Gnostics, who claimed to have a secret oral tradition directly from Jesus himself. Against such claims, Irenaeus argues that the bishops in different cities were known back to the Apostles—and none of them were Gnostics—and that the bishops provided the only sure guide for the interpretation of Scripture. With these lists of bishops, the later doctrine of the "apostolic succession" of bishops could be established. Even the unique position of authority of the bishop of Rome is emphasized by Irenaeus, albeit obscurely.
Although there is no evidence, other than legendary, regarding his death, the last decade of the 2nd century is generally considered to be the period of Irenaeus' death.