Nativity by Theodotus of Ancyra.

Splendid and wonderful is the object of today’s solemnity! Splendid, because it offers common salvation to men; wonderful, because it surpasses the laws of nature. For nature does not know any woman who both gave birth and remained a virgin; it is grace that made her bear and conserved her virginity. Grace made the Mother and did not damage her virginity. In truth, it was grace that guarded her chastity.

O unsown field, from which sprouted a saving fruit! O Virgin, surpassing the Garden of Eden itself! For young plants of every kind were born in Eden, springing up from the virgin soil; yet this Virgin is better than that soil. She does not make fruit trees grow but the root of Jesse, which gives the saving fruit to men. The first soil was virgin; so is this new soil. In Eden, God decreed that plants should be born; in this Virgin, the Creator himself became a sapling, according to the flesh. The first garden yielded no produce before the plants came; nor was Mary’s virginity diminished by Christ’s] birth.

The Virgin became more glorious than paradise. Indeed, this was God’s cultivating; according to the flesh, God cultivated her, desiring to unite himself with human nature.
Have you seen how marvelous was the mystery, transcending the law of nature? Have you seen this supernatural occurrence, wrought by the power of God alone? Have you seen the Word beyond words being born? The fact that he did not destroy her virginity plainly shows that the One born is the Word of God. A woman who gives birth to mere flesh ceases to be a virgin; but the Word of God, born in the flesh, maintains her virginity, thus showing that he is the Word. And when you hear me say “Word” (understand that I mean the substantial and subsistent Word, not the word one speaks forth with one’s mouth.

And so the only begotten Son of God is born, who is also called the Word. He does not begin to exist as the Word from the moment of this birth; rather, he makes this birth the principle of his becoming man. Indeed, God the Word existed before all ages, coeternal with
the Father. But when he wished to become man out of love for men, he chose birth as the principle of his becoming man, not through a change in his divine nature, but through a miracle according to the will of God. Therefore, he was born as man; he kept intact her virginity as Word. For, just as our words are born without corrupting our minds, so the substantial and subsistent Word of God, in experiencing birth, does not corrupt [his Mother’s] virginity.

This birth, then, surpasses the laws of nature. So do not lower yourself to the level of the ways of nature. I am presenting you with a miracle; do not put forth a line of reasoning. I tell you that it involves a birthed God who has chosen to be born; yet this birth was not the beginning of his existence in his divinity. Being God, he took a birth to himself, but it was not the birth that made him God. Wanting to become what he was not, nevertheless he remained what he had been. He chose the birth as the principle of the Incarnation. He became man without altering his nature, without eliminating the elements of the divine substance.

Theodotus of Anchyra ,
Homily I on the Nativity of the Lord 1-2; PG 77, 1349-52