Christian faith can so easily slide into a head-only existence. Christianity lives in a tension between flesh and ascesis. When it loses that balance, Christianity often slides into a disregard of the flesh. Sometimes this disregard takes the form of benign neglect, sometimes an active hostility towards the material world.
The celebration of Christ's birth continually pulls us back to the material world, to the flesh we have in common with everyone else, and now with God as well.
