Irenaeus is above all a man of faith and a pastor. Like the Good Shepherd, he has prudence, a richness of doctrine, and missionary zeal. As a writer, he aims for a twofold objective: to defend true doctrine from the attacks of the heretics, and to clearly expound the truth of the faith. His two works still in existence correspond exactly to the fulfillment of these two objectives: the five books "Against Heresies," and the "Demonstration of Apostolic Preaching" (which could be called the oldest "catechism of Christian doctrine"). Without a doubt, Irenaeus is the champion in the fight against heresies.
The Church of the second century was threatened by so-called gnosticism, a doctrine which claimed that the faith taught by the Church was nothing more than symbolism for the simpleminded, those unable to grasp more difficult things. Instead, the initiated, the intellectuals -- they called themselves gnostics -- could understand what was behind the symbolism, and thus would form an elite, intellectual Christianity.
Obviously, this intellectual Christianity became more and more fragmented with different currents of thought, often strange and extravagant, yet attractive to many. A common element within these various currents was dualism, that is, a denial of faith in the only God, Father of all, creator and savior of humanity and of the world. To explain the evil in the world, they asserted the existence of a negative principle, next to the good God. This negative principle had created matter, material things.
Firmly rooted in the biblical doctrine of Creation, Irenaeus refuted dualism and the gnostic pessimism that devalued corporal realities. He decisively affirmed the original holiness of matter, of the body, of the flesh, as well as of the spirit. But his work goes far beyond the refutation of heresies: In fact, one can say that he presents himself as the first great theologian of the Church, who established systematic theology. He himself speaks about the system of theology, that is, the internal coherence of the faith.
The question of the "rule of faith" and its transmission lies at the heart of his doctrine. For Irenaeus, the "rule of faith" coincides in practice with the Apostles' Creed, and gives us the key to interpret the Gospel, to interpret the creed in light of the Gospel. The apostolic symbol, a sort of synthesis of the Gospel, helps us understand what the Gospel means, how we must read the Gospel itself.
In fact, the Gospel preached by St. Irenaeus is the one he received from Polycarp, bishop of Smyrna, and the Gospel of Polycarp goes back to the apostle John, Polycarp having been John's disciple. Thus, the true teaching is not that invented by the intellectuals, rising above the simple faith of the Church. The true Gospel is preached by the bishops who have received it thanks to an uninterrupted chain from the apostles.
These men have taught nothing but the simple faith, which is also the true depth of the revelation of God. Thus, says Irenaeus, there is no secret doctrine behind the common creed of the Church. There is no superior Christianity for intellectuals. The faith publicly professed by the Church is the faith common to all. Only this faith is apostolic, coming from the apostles, that is, from Jesus and from God.
Some may be familiar with St. Irenaeus as his writings were often mentioned in the refutation of The DaVinci Code. During the whole dust up surrounding The DaVinci code, I became convinced that my own woeful ignorance of Church history, especially the first few centuries of the Church, was a common state among Catholics. Obviously Pope Benedict agrees. He is dedicating his General Audiences to addressing this deficiency.
I would like to recommend some reading options to help with this task. Ten Dates Every Catholic Should Know and What Every Catholic Wants to Know, both by Diane Moczar, are short, easy-to-read, treatises on Catholic Church History. Alan Schreck’s The Compact History of the Catholic Church is another very good introduction to Church history. This book is used by my daughter’s CCD high school CCD class. She is not a fan of history in general but found this book as well as the class enjoyable and informative.