Irenaeus of Lyons (ca. 130-202) began to theologize at a crucial period in the history of the church. It was a bit of a mess.
From the earlier apologists he inherited a vocabulary of Greek philosophical terms with Christian significance. At the same time, Gnostics of various kinds were beginning to appropriate the words of the Christian confession and apply them to their own pantheons of heavenly powers. So Christians were developing the ability to talk like philosophers, and Gnostics were doing their best to talk like Christians. For a time there in the second century, everyone must have seemed to be using everyone else’s words, speaking the same composite language to say altogether different things. Everyone was saying something about God, and Irenaeus’ task was to mark off the distinctive claim of Christian theology, in order to make clear its message about God.
One way to view the trend of second-century theologies is as an unravelling of the unity of the concept of God. Marcion distinguished the God of the Old Testament from the God who is the Father of Jesus Christ. Gnostics of the Valentinian school (among others) claimed to see beyond the God who created heaven and earth, the Demiurge, to the ineffable Absolute One who stood at the top of a long line of Aeons. Irenaeus’ task was to demonstrate that all these different ideas about God/gods were in fact fractured attempts to speak about the one true God, as confessed by the Christian Church. The idea of God was bursting apart at the seams, and Irenaeus had to stuff all the various alternative Gods back into a single package.
The way he did this was to argue from the continuity of revelation, beginning with the two-testament unity of Scripture and moving out into the unity of the Christian confession. Irenaeus developed his theology of the apostolic transmission of truth partly with a view toward guaranteeing the unity of the God preached by the Church. The God who created heaven and earth is the God of the Old Testament, and this same God sent his Son in the fullness of time, as the Word become flesh. The prophets foretold his coming, the apostles saw him and lived with him, and the present church continues to speak of him with the same single voice. In this way, Irenaeus united the medium of proclamation with the message proclaimed: The Church speaks of one God in one voice. That voice includes the prophets and apostles and the lineage of post-apostolic teachers.
The unity of the tradition has three implications:
1. It means the God spoken of at all times in the tradition is one, thereby bridging the diverse periods of salvation history.
2. It means that the ideas involved all belong together in a single authoritative chain or mosaic.
3. It means that language about God which does not partake of this tradition probably does not mean the same thing, even if it uses some of the same words, since the truth in Christ is a concrete individual occurrence and not a general truth.
By anchoring his theology to a historical line of tradition, Irenaeus insured that there was a definite way to determine which God was being indicated. The God who is the Father of Jesus Christ is proclaimed by a certain lineage of apostles, prophets, and bishops. All the various aspects under which he could be viewed are to be united in this one proclamation. The Demiurge is the God of the Old Testament is the Father of Jesus Christ is the One God described in Christian preaching.
By concentrating on the historical acts of God, in the salvation history which reaches its climax in Christ, the theology of Irenaeus reaches a new high point in early Christian theology. Compared to earlier writers like the Apostolic Fathers, he shines. Authors like Ignatius, Clement, and Barnabas had understood the Christian message in its entirety, but had especially emphasized the ethical or imperative side of it. For Clement of Rome, everything seems to end up simply as a reminder to do good, or an instruction about avoiding evil. Irenaeus developed the proclamation side of the Christian message, concentrating on retelling the story of God’s redemptive act in Christ. While all the elements were present in an author like Clement (apostolic succession, memory of Christ, etc), they actually come to life and breathe in the theology of Irenaeus. This natural inclination of his theology of apostolic proclamation restored to Christian proclamation some of the liveliness of the New Testament’s own message; Irenaeus’ own work was in fact its own kind of “demonstration of the apostolic preaching.”