Really, the Advent season runs from Genesis 3 onward, and Christmas Day is when the miracle prophesied in Luke 1:35 is fulfilled. For those of us who believe personhood can be derived from Psalm 139:13-15 and Job 31:15, we believe the Incarnation did not begin at Jesus' birth but at his conception. And if this is so, when Colossians 2:9 says, "For in him the whole fullness of deity dwells bodily," we know that the fullness of deity dwelled in fertilized ovum.
Will the Empire State Building occupy a doghouse? Will a killer whale fit inside an ant?
And here we are told that omnipotence, omniscience, omnipresence, utter eternalness and holiness dwelled in a tiny person. This makes Santa coming down a chimney seem a logistical cakewalk.
"The head of all rule and authority" (Col. 2:10) had one of those jelly-necked wobbly baby heads. The government rested on his baby-fatted shoulders (Is. 9:6).
This miracle of addition is important. We must hold it tightly or lose the bigness of the Incarnation. God came as unborn child so that Christ would experience all of humanity. And he experienced all of humanity so that we might receive all of him for all of us.
If God came as a vulnerable, needful, weak baby, we have no need to fear for our own vulnerability, needfulness, and weakness. He emptied himself (Phil. 2:7) so that we would not see our own emptiness as a hopeless cause. "As you received him"—desperate, helpless, desirous—"so walk in him" (Col. 2:6). The miracle of the God-Baby proclaims the gospel's specialty: rescue of the helpless.