I've been brushing up on my Patristics over the last couple of weeks, with the help of John Behr's books on the formation of Christian Theology. It's been really useful stuff. One of the things that has been driven home to me is that the foundational question of Christian Theology is 'does Jesus Christ reveal God?' Of course, it's possible that I'm reading things through this lens because I think that this is the central question to be asked and answered today; still, Behr does indicate that this is at the heart of discussions in the first four centuries of the Church as well. Indeed, he structures his discussion of the Fathers' doctrine around the gospel question 'who do you say I am?' - with each theologian giving subtly different answers.
An interesting contrast drawn by Behr is between Justin Martyr and Irenaeus of Lyons. Both are generally considered to be orthodox, which makes the comparison all the more interesting - we are not dealing with wild heresies, but with a discussion within the Great Church. Behr argues that for Justin, who never quite escapes his Platonist past, it is a presuppositional truth that God is utterly transcendent, and therefore not capable of being seen. He understands Christ as a second God, a visible God. He is not at this point heading into ditheism; he believes in, although he doesn't particularly develop, the oneness of the Father and the Son. But he does apply titles to Christ which would later drop out of use - he calls him an apostle and an angel. It wouldn't be too hard to show Scriptural support for both titles, but in Justin's theology they show the place of the Son: he bridges the gap between the Father and the creation, as a messenger. This enables Justin to see significant continuity between the Son and creation, and to claim all truth - even when uttered by pagan philosophers - as the Word of God. "[F]or Justin, the revelation of God in the Incarnate Word is the last, even if the most important, in a series of discrete revelations" (Behr). Moreover, for Justin the Word reveals the Word - God the Father, in his incomprehensible transcendence, remains essentially unknown.
For Irenaeus, on the other hand, there is no division between the Father and the Son; although distinct, they are absolutely united. The Son reveals the Father - "the Father is the invisible of the Son, the Son is the visible of the Father" (Against Heresies). The Son is not conceived of as a bridge (which in the end leads nowhere), but as the manifestation of the Father himself. The continuity between the Son and creation which creeps in to Justin is absent; God is revealed only in Christ, the incarnate Word, and not elsewhere. Where for Justin, the Son/Word as intermediary between God and creation can be seen throughout creation and only supremely in Christ, for Irenaeus the Son is seen in Christ alone. The incarnation, death, and resurrection of Christ are the revelation of God. Prior revelation, to the patriarchs and through the Scriptures, is to be understood as related prophetically to the incarnate Word. There is no room here for any logos asarkos.
It is interesting that the debates about Christology that developed long after Justin and Irenaeus were safely home would revolve initially around whether Christ really is God and therefore able to reveal God, and then around whether this happens in real humanity. It is all about whether God can be known, and how he can be known. The answer the orthodox arrived at in the fourth century is that God can be known, but only in his Son, who as true God truly reveals God, and further that the Son can only be seen as incarnate, crucified, and risen, as a true human being. That, for me, is the crux of all Christian theology: is God seen in Christ, and him crucified? Is he seen there truly? Is he seen there alone?