By far the greatest anti-heretical writer—indeed, the greatest second-century theologian—was St. Irenaeus of Lyons. Irenaeus is sometimes called the father of Catholic theology because of the comprehensive detail in which he explained and defended the articles of the true faith. He did this in the course of his other main achievement: dealing a mortal blow to Gnosticism.
The “gnosis falsely so-called” against which Irenaeus directed his main treatise was a product of intellectual speculation unbounded by humility. The heretics wanted to create a version of Christianity suitable to their own intellects; they pretended to have discovered a new and higher doctrine which superseded the revelation of the New Testament, which they considered full of “symbols for the symbol-minded” (to borrow a pun from the atheist comedian George Carlin). So they embellished doctrines to please their finite and puffed-up intellects, inventing convoluted systems of divine beings beyond the God of revelation.
For Irenaeus, though, everything comes down to the one rule of faith which all Christians hold in common. This is the universal teaching handed down unaltered from the Apostles, the canon of faith stated in the baptismal creed.
If the apostolic tradition preserves the same faith for all, then intellectuals cannot improve upon it nor can the simple-minded take away from it. Pope Benedict XVI said in an address on St. Irenaeus:
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.
While Irenaeus emphasized tradition and was not one for speculative theology, neither was his faith static and formalized. Benedict again illuminates his thought for us:
For Irenaeus, Church and Spirit were inseparable: “This faith”, we read again in the third book of Adversus Haereses, “which, having been received from the Church, we do preserve, and which always, by the Spirit of God, renewing its youth as if it were some precious deposit in an excellent vessel, causes the vessel itself containing it to renew its youth also…. For where the Church is, there is the Spirit of God; and where the Spirit of God is, there is the Church and every kind of grace” (3, 24, 1). As can be seen, Irenaeus did not stop at defining the concept of Tradition. His tradition, uninterrupted Tradition, is not traditionalism, because this Tradition is always enlivened from within by the Holy Spirit, who makes it live anew, causes it to be interpreted and understood in the vitality of the Church.