Saint Irenaeus is the saint of the day, the vigil of Saints Peter and Paul. He was bishop of Lyons in what is now France, a doctor of the Church, and venerated as a martyr for the faith (+202), a disciple of fellow martyr Saint Polycarp (+155), who in turn was learned the faith at the feet of Saint John the Beloved.
Besides his holy and apostolic life, consolidating the early Church, Irenaeus is most famous for his erudite and forceful treatise Adversus Haereses (Against Heresies) which put paid to, and more or less destroyed forevermore, the heresy of Gnosticsm, which taught that only an inner, enlightened ‘few’ could understand Christ’s teaching, which the Gnostics interpreted according to their own ‘reason’ (as well as their misguided emotions and desires), unhinged from Tradition (as well as Scripture).
It fell to the sharp and disciplined mind of Irenaeus to make clear that the only true teaching is the one that comes from the Apostles, found in Tradition, which in turn is taught and handed on by the One, Holy, Catholic and Apostolic Church of Rome. Anything that deviates from that consistent teaching is a ‘heresy’, a division, a wound in the Mystical Body, to which one cannot assent, and which cannot be left to fester. His own consolidation of the traditional teaching of the Church earned him the title of Doctor, a universal teacher of the faith. In fact, he is often venerated as the founder of the whole science of ‘theology’, that whole unpacking and explaining of revelation according to properly ordered reason and tradition.
As Pope Benedict put it in his own 2007 reflection on Irenaeus (well worth a read):
The true teaching, therefore, is not that invented by intellectuals which goes beyond the Church’s simple faith. The true Gospel is the one imparted by the Bishops who received it in an uninterrupted line from the Apostles. They taught nothing except this simple faith, which is also the true depth of God’s revelation. Thus, Irenaeus tells us, there is no secret doctrine concealed in the Church’s common Creed. There is no superior Christianity for intellectuals. The faith publicly confessed by the Church is the common faith of all.
We don’t know a lot of Irenaeus’ death, but he was and is venerated as a martyr for the truth, a cause to which he dedicated his entire life. May we all follow his example, for only the truth will set us free.