Icon of St. Irenaeus
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In Book I, Irenaeus talks about the Valentinian Gnostics and their predecessors, who go as far back as the magician Simon Magus
In Book II, Irenaeus proves that Valentinian Gnosticism has no merit.
In Book III, Irenaeus purports to show that these doctrines are false by providing counter-evidence from the Gospels.
In Book IV, Irenaeus stresses the sayings of Jesus and the unity of the Old Testament with the Gospel.
In Book V, Irenaeus focuses on more sayings of Jesus and also the letters of Paul the Apostle.
Irenaeus was born during the first half of the 2nd century (the exact date is disputed: between the years 115 and 125 according to some, or 130 and 142 according to others), and he is thought to have been a Greek from Polycarp’s hometown of Smyrna in Asia Minor, now İzmir, Turkey. Unlike many of his contemporaries, he was brought up in a Christian family rather than converting as an adult.
During the persecution of Marcus Aurelius, the Roman Emperor from 161–180, Irenaeus was a priest of the Church of Lyon. The clergy of that city, many of whom were suffering imprisonment for the faith, sent him in 177 to Rome with a letter to Pope Eleuterus concerning the heresy Montanism, and that occasion bore emphatic testimony to his merits. While Irenaeus was in Rome, a massacre took place in Lyon. Returning to Gaul, Irenaeus succeeded the martyr Saint Pothinus and became the second Bishop of Lyon.
During the religious peace which followed the persecution of Marcus Aurelius, the new bishop divided his activities between the duties of a pastor and of a missionary (as to which we have but brief data, late and not very certain). Almost all his writings were directed against Gnosticism. The most famous of these writings is Adversus haereses (Against Heresies). Irenaeus alludes to coming across Gnostic writings, and holding conversations with Gnostics, and this may have taken place in Asia Minor or in Rome. However, it also appears that Gnosticism was present near Lyon: he writes that there were followers of ‘Magus the Magician’ living and teaching in the Rhone valley.
Little is known about the career of Irenaeus after he became bishop. The last action reported of him (by Eusebius, 150 years later) is that in 190 or 191, he exerted influence on Pope Victor I not to excommunicate the Christian communities of Asia Minor which persevered in the practice of the Quartodeciman celebration of Easter.
Nothing is known of the date of his death, which must have occurred at the end of the 2nd or the beginning of the 3rd century. A few within the Roman Catholic Church and Orthodox Church celebrate him as a martyr. He was buried under the Church of Saint John in Lyon, which was later renamed St Irenaeus in his honor. The tomb and his remains were utterly destroyed in 1562 by the Huguenots.
Irenaeus wrote a number of books, but the most important that survives is the Against Heresies (or in its Latin title, Adversus Haereses). In Book I, Irenaeus talks about the Valentinian Gnostics and their predecessors, who go as far back as the magician Simon Magus. In Book II he attempts to provide proof that Valentinianism contains no merit in terms of its doctrines. In Book III Irenaeus purports to show that these doctrines are false, by providing counter-evidence gleaned from the Gospels. Book IV consists of Jesus’ sayings, and here Irenaeus also stresses the unity of the Old Testament and the Gospel. In the final volume, Book V, Irenaeus focuses on more sayings of Jesus plus the letters of Paul the Apostle.
The purpose of “Against Heresies” was to refute the teachings of various Gnostic groups; apparently, several Greek merchants had begun an oratorial campaign in Irenaeus’ bishopric, teaching that the material world was the accidental creation of an evil god, from which we are to escape by the pursuit of gnosis. Irenaeus argued that the true gnosis is in fact knowledge of Christ, which redeems rather than escapes from bodily existence.
Until the discovery of the Library of Nag Hammadi in 1945, Against Heresies was the best-surviving description of Gnosticism. According to some biblical scholars, the findings at Nag Hammadi have shown Irenaeus’ description of Gnosticism to be largely inaccurate and polemic in nature. Though correct in some details about the belief systems of various groups, Irenaeus’ main purpose was to warn Christians against Gnosticism, rather than catalog those beliefs. He described Gnostic groups as sexual libertines, for example, when some of their own writings advocated chastity more strongly than did orthodox texts—yet the gnostic texts cannot be taken as guides to their actual practices, about which almost nothing is reliably known today. In any case the gnostics were not a single group, but a wide array of sects. Some groups were indeed libertine because they considered bodily existence meaningless; others praise chastity, and strongly prohibited any sexual activity, even within marriage. Rodney Stark asserts that it is the same Nag Hammadi library that proves Irenaeus right.
Irenaeus also wrote The Demonstration of the Apostolic Preaching (also known as Proof of the Apostolic Preaching), an Armenian copy of which was discovered in 1904. This work seems to have been an instruction for recent Christian converts.
Eusebius attests to other works by Irenaeus, today lost, including On the Ogdoad, an untitled letter to Blastus regarding schism, On the Subject of Knowledge, On the Monarchy or How God is not the Cause of Evil.
Irenaeus exercised wide influence on the generation which followed. Both Hippolytus and Tertullian freely drew on his writings. However, none of his works aside from Against Heresies and The Demonstration of the Apostolic Preaching survive today, perhaps because his literal hope of an earthly millennium may have made him uncongenial reading in the Greek East. Even though no complete version of Against Heresies in its original Greek exists, we possess the full ancient Latin version, probably of the third century, as well as thirty-three fragments of a Syrian version and a complete Armenian version of books 4 and 5.
Irenaeus’ works were first translated into English by John Keble and published in 1872 as part of the Library of the Fathers series.
Irenaeus is also known as one of the first theologians to use the principle of apostolic succession to refute his opponents.
In his writing against the Gnostics, who claimed to possess a secret oral tradition from Jesus himself, Irenaeus maintained that the bishops in different cities are known as far back as the Apostles and that the bishops provided the only safe guide to the interpretation of Scripture. In a passage that became a locus classicus of Catholic-Protestant polemics, he cited the Roman church as an example of the unbroken chain of authority which text Western polemics would use to assert the primacy of Rome over Eastern churches by virtue of its preeminent authority.
With the lists of bishops to which Irenaeus referred, the doctrine of the apostolic succession, firmly established in the Church at this time, of the bishops could be linked. This succession was important to establish a chain of custody for orthodoxy. He felt it important, however, to also speak of a succession of elders (presbyters).
Irenaeus’ point when refuting the Gnostics was that all of the Apostolic churches had preserved the same traditions and teachings in many independent streams. It was the unanimous agreement between these many independent streams of transmission that proved the orthodox Faith, current in those churches, to be true.
Irenaeus of Lyons: Identifying Christianity (Christian Theology in Context) by Fr John Behr
Irenaeus of Lyons (The Early Church Fathers) by Robert M. Grant
Of God and Man: Theology as Anthropology from Irenaeus to Athanasius by M. C. Steenberg
The Biblical Theology of Saint Irenaeus by John Lawson
Irenaeus of Lyons by Eric Osborn
Man and the Incarnation: A Study in the Biblical Theology of Irenaeus by Gustaf Wingren