The laws of nature are changed
Today our Lord Jesus Christ, who is for ever the creator of all things, has become saviour for us by being born of a mother. Today by his own free will he was born for us in time, that he might lead us to the eternity of the Father. God was made man that man might become God; that man might partake of the bread of angels, the Lord of angels was today made man.
Today the prophecy has been fulfilled: Pour down dew, ye heavens, from above, and let the clouds rain justice: let the earth open, and let it bring forth a saviour. Therefore he who had made was himself made that he who had been lost might be found. This is what man confesses in the Psalms: Before I was brought low, I sinned. Man sinned, and was made the accused: God was born as man that the accused might be freed. Man therefore fell down but God came down. Man fell pitifully, God came down in pity: man fell through pride, God descended with grace.
My brethren, see what miracles and wonders are here. The laws of nature are changed in a man; God is born, a virgin conceives without a man: the Word of God plays a husband’s part to one who knows not a man: she becomes at the same time mother and virgin; made a mother and yet uncorrupted, a virgin having a son, and yet not knowing a man, ever sealed, and yet not barren. For he alone was born without sin whom she brought forth without a husband’s embrace, not by the desire of the flesh, but by the obedience of the mind.
St Augustine, Sermon 13
On the Seasons