It's the idea that the creator of the universe physically entered his own creation in order to set aright that which had gone wrong -- to heal a wound.
That's no modest claim.
The Danish philosopher Søren Kierkegaard (1813-1855) called faith in the Incarnation a commitment to the absurd. (Source; More)
The French poet and playwright Paul Claudel (1868-1955) penned this tongue-in-cheek take on the Incarnation:
-- from “I Believe in God, A Meditation on the Apostles Creed.”
“When God took possession of the human form, when he appropriated it for his own use, when he placed himself within it in hypostatic union, he committed an unpardonable offense against justice, good sense and propriety. Until the end of time, intellectuals will respond with alternating indignation and amusement. There are certain things that are simply not done. … this transgressor caught in the very act of stealing back a possession we had every reason to regard as exclusively ours.
… He embezzled our funds for his own profit. In one stroke he reclaimed for his Father all that cultivated estate which we considered ours by tenants’ rights, under the terms of a hard-won agreement. …
Thanks to the complicity of the Virgin, there has been a stealthy raid on our nature. The damage is permanent; henceforth our walls are marred by a crack that for all our industry can never be mended again. … Our homes are no longer our own.”
The image above is a detail of "The Nativity" (c. 1303-1306) by Giotto di Bondone.