Ben: In NT studies one often hears the old canard that you can’t find the Trinity in the NT. I myself think you can certainly find the assertion or direct implication that Father, Son and Spirit should all be called God and Lord in the NT, so at least we have the raw data for Trinitarian thinking in the NT. How does Irenaeus think about this subject, and would you say he is mainly indebted to the Scriptures in his thinking on this, or mainly indebted to Greek philosophy, or does he simply follow the lead of other church fathers like Tertullian who appears to have coined the phrase Trinitas?
Jackson: Irenaeus is thoroughly grounded in scripture. He emphasizes that scripture must be read in accordance with the teaching of the apostles and the elders, what is broadly called the regula fidei or the rule of faith. One of the open questions in Irenaean studies is just who these influences are. He references Justin Martyr and there is compelling evidence that he also read and was influenced by Theophilus of Antioch, but in terms of Trinitarian theology, he is quite different than these folks and the people he more resembles, arguably Tertullian, actually come after him. He is quite dismissive of Greek philosophy and so-called speculative theology because he views these as part of the causes of the Gnostic errors. While he actually has a lot to say about speculative issues, such as who God is apart from creation (the so-called immanent Trinity), and he is more competent with Greek philosophy than he lets on, neither of these influences can fully account for his Trinitarian theology.
As I show in the book, the logic that drives this account of scripture demands a Trinitarian understanding of God, however different the language is from later fourth century formulations. Irenaeus places the Son and the Spirit on the side of God in the Creator/creature divide. Like the Father, the Son and the Spirit are eternal, uncreated, and participate in the divine acts of creating the world and redeeming the world. Indeed, far from being a lesser divine being—as the Gnostics again believed—Irenaeus affirmed that the Son’s full divinity is necessary to save creation. The Son reveals the Father because, like the Father, he is God himself. To paraphrase Irenaeus, “He became what we are to make us what he is.”