As we recite the words “He was incarnate of the Virgin Mary and became man”) something happens in the liturgy that is worth noting. On most days of the year when the Creed is said, every member of the congregation (assuming they have been properly catechized) takes what is known as a “profound bow”: that is, a bow from the waist. On Christmas Day, the congregation kneels at these words. Why? Because the liturgy teaches us through gesture to make our flesh a participant in the memorial of the Incarnation as we declare with our mouth that the Word became flesh. Just as the Son of God humbled himself to become flesh, so we, with our bodies, humble ourselves too by bowing or kneeling in memory of his humiliation.
The book of Hebrews takes a passage from the Psalms and places it on the lips of Jesus to summarize the why of this act of self-humiliation by God:
[W]hen Christ came into the world, he said,
“Sacrifices and offerings you have not desired,
but a body have you prepared for me;
in burnt offerings and sin offerings you have taken no pleasure.
Then I said, ‘Behold, I have come to do your will, O God,’” (Hebrews 10:5-7)
This captures perfectly the early Church’s understanding of the reason God the Son became man: to do the will of the Father as man. The logic is as simple as it is astounding: No Mary, no human nature for God the Son to assume. No human nature, no death on the cross. No death on the cross, no resurrection from the dead. No resurrection, no salvation. The Incarnation is the utterly necessary prelude to the entire drama of redemption. And it begins (in time, at any rate) at the Annunciation when Mary’s utterly free “Yes” is offered to the God who has willed the Incarnation from all of eternity. Given the omnipotence of God, most people can grant, in theory, that he can do as he pleases and take on human flesh. But throughout the history of the Church, there have been people who still found the doctrine incredible for a host of reasons. The proposition is, after all, that God, the invisible power that hurled the universe into being and invented DNA and holds quarks together and spoke to prophets and parted the Red Sea and knows everything and can do everything—that God–somehow joined himself to a single cell in the womb of a creature with a digestive tract built on the same basic model as that of an earthworm, with blood reflecting the same salinity levels as the seawater from which life sprang, bearing a nervous system, endocrine glands, musculature and a gene array that is made of the same sort of stuff as the rest of the animal kingdom. God became a creature whose diapers had to be changed. That is the Christian claim. And if it doesn’t shock you, you haven’t been listening.