Just a last quick Christmas thought before the decorations come down tonight.
I don't think we understand the incarnation. To put it more strongly, I don't think we can understand the incarnation. Think about what we say: we say that God became a man, took on flesh, clothed himself in our nature. I think it's quite possible to understand some or all of these words and concepts - but is it really possible to grasp what they actually indicate? Can we really have any understanding of what it means to say that God becomes a human being?
It's interesting to read the history of christological controversy in the early church as an attempt to understand this - and it is interesting that orthodoxy, as far as I can tell, always comes down on the incomprehensible side. The heretics are trying, as a rule, to simplify things, or at least to bring them within the realm of things we might be able to grasp. What is Arianism, after all, but an attempt to make the incarnation a bit less incomprehensible? Arius does it by making the incarnate actually something less than God, and in so doing seems to avoid the apparent category mistake of the orthodox, who insist that it is actually God, the invisible God, who appears in the human nature of Christ.
Or the various disputes about the natures and will of Christ. The monophysites want to make Christ a mix of divine and human (actually, whether they wanted to do this is debatable; certainly their theological descendants would repudiate this project. But that is the tendency which the orthodox thought they saw in monophysite thought). Although that is still pretty hard to understand, it does at least mitigate the harshness of saying that Christ is at once infinite and finite, invisible and visible, God and man. A blend is easier to comprehend, but it is heretical. On a less ontological and more psychological point, the monothelite want to give Christ but one will, the divine will standing in for the human. Simpler, sort of makes sense. But the orthodox insist that Christ has two wills, divine and human - even though this makes it more or less impossible for us to imagine or comprehend his inner life.
The point is that we don't understand, and that has to be okay. If we understood, it wouldn't be God-in-the-flesh. Our concepts can do nothing more than point us to the reality, which is Christ; that's why in Christian theology the story is prior to the concepts, which can only serve it.