The importance of Irenaeus’s work is that here we have a writing which may be considered the beginning of orthodoxy after the doctrinal chaos of the previous half-century. He gives us a lucid and detailed statement of the basic truths of faith, God, Christ and salvation. From the earlier period the fullest post-apostolic exposition of the Christian faith we possess is Justin Martyr’s writing, particularly his Dialogue with Trypho the Jew (c. AD 135). Obviously the dialogue with a Jew is more restricted, directed to one particular matter, the incarnation and messiahship of Jesus. Irenaeus knew and admired this work, written half a century earlier, and clearly made use of it; on occasion his arguments run on lines parallel to it. Justin is a philosopher, and I think Irenaeus also has a philosophical turn of mind, enjoying the same sort of philosophical argumentation and logic, though he can also burst into prayer on occasion. But Irenaeus faces a different problematic. In the second century a new situation had arisen: the influx into Christianity of gentiles of a classical background. They attempted to understand Christ and Christianity in terms of their own background, losing touch to an extraordinary extent with the Jewish background of Christianity.
For Irenaeus himself this blindness to the Jewish background has important consequences, both negative and positive. Negatively, he shows striking ignorance of Hebrew, hence an extraordinary passage in which he gives etymologies of the divine names Sabaoth, Elohim, Adonai and the sacred Tetragrammaton, which show total ignorance of Hebrew. He also dizzily thinks (Demonstration, 43) that the two first words of the book of Genesis, breshith bara (‘In the beginning he created’), include the word ‘son’. In 3.8.1 he carefully, but quite incorrectly, insists that mamuel (which he thinks is the Hebrew for the Aramaic mammon in Lk 16:13) means ‘glutton’; there is no such word in biblical Hebrew.
On the positive side, ignorance of the Hebrew Bible is a considerable help to Irenaeus in his proof of the divinity of Jesus, which he argues uniquely on the basis of the Greek text of the Bible. He exclusively uses the Greek Septuagint translation, which he argues with persuasive competence to be inspired. From the earliest days this translation, stemming from the Greek-speaking Jews of Alexandria, had been the Bible of the Christian Church. It is the text of the Old Testament used consistently in quotation of the Old Testament in the New. It was not until two centuries later—and not without considerable opposition—that St Jerome hit on the idea of using the Hebrew as the basic text. Hence for Irenaeus wherever the Greek kyrios occurs it refers to the LORD God. In fact it sometimes translates the sacred Tetragrammaton (YHWH, ‘the Lord’), but sometimes means far less: ‘the lord’, a title merely of respect, not of worship. In the vocative it can mean merely ‘Sir’! The use of kyrios for Jesus is an important element in his strong Christology: Jesus is the LORD God tout court. The later subtleties made possible by the distinction of the terms ‘person’ and ‘nature’ have not yet evolved and were therefore unavailable to Irenaeus. They are, of course, a feature of the controversies of the fourth century that led to clarification of the philosophy implied by the doctrine of the Trinity. These philosophical discussions had not yet developed in the Church. Without these subtleties, Irenaeus reads Lk 2:11 (‘Today is born to you a saviour who is Christ the Lord’) as ‘Christ the Lord’, an unambiguous affirmation of the human birth of God.
