One of my favorite saints is honored in the church today. I loved reading "Against Heresies" long before I became a Catholic. In fact reading Irenaeus and other very early Christian writers is what convinced me the Church has ALWAYS been Catholic. Irenaeus was taught by Polycarp, who was taught by the Apostle John, so he is very close to the first generation of Christians.
From Universalis today:
Irenaeus was born in Smyrna, in Asia Minor (now Izmir in Turkey) and emigrated to Lyons, in France, where he eventually became the bishop. It is not known for certain whether he was martyred or died a natural death.
Whenever we take up a Bible we touch Irenaeus's work, for he played a decisive role in fixing the canon of the New Testament. It is easy for us, now, to think of Scripture – and the New Testament in particular – as the basis of the Church, and harder to remember that it was the Church that had to decide, early on, what was scriptural and what was not.
Before Irenaeus, there was vague general agreement on what scripture was, but a system based on this kind of common consent was too weak. As people meditated on the intolerable event of the Redemption, dissensions and heresies inevitably arose, and reference to scripture was the obvious way of trying to settle what the truth really was. But in the absence of an agreed canon of scripture it was all to easy to attack one's opponent's arguments by saying that his texts were corrupt or unscriptural; and easy, too, to do a little fine-tuning of texts on one's own behalf.
So Irenaeus went through all the books of the New Testament, and all the candidates (such as the magical pseudo-Gospels, and the entertaining and uplifting novel the Shepherd of Hermas). He did not simply accept or reject each book, because his enemies could have said that he was doing it to bolster his own arguments: he gave reasons for and against the canonicity of each book. Irenaeus's canon of scripture is very nearly the modern one (he does not quote from three of the short universal epistles), but more important is the fact that he started the tradition of biblical scholarship.
Irenaeus had to fight against the Gnostics, who believed that the world was irredeemably wicked, and against the Valentinians, who claimed to be possessors of a secret tradition that had never been written down but passed from master to disciple through the ages. This pessimism and this arcane élitism remain with us even today, and each generation must renew the fight against them. Let us pray for the inspiration of St Irenaeus in our battle.
I have learned in whatever situation I am to be content.