Wisdom of Saint Leo the Great

"Our Lord Jesus Christ, descending from His throne in Heaven, but leaving not that glory which He has with the Father, cometh into this world here below by being born after a new order and in a new birth. He cometh after a new order, in that He who is invisible in His own nature was visible in ours. The Incomprehensible desired to be comprehended, and He that is from everlasting to everlasting began to be in time. He was the Offspring of a new birth: He was conceived of a virgin, without the passion of any fatherly flesh, without any breach of His Mother's virginity, since such a birth was fitting for the coming Saviour of mankind, who was to have in Him the nature of man's being, but to be free of any defilement of man's flesh. Though His origin is unlike ours, yet with us He shares alike in our nature. For, though we believe that His birth lacked the usual and customary fashion of conception among mankind, yet it was the power of God which wrought that a [human] maiden should conceive [a human Son], but that a maiden should give birth, and that a maiden she should abide still."

--St. Leo the Great, Pope, from Sermon 2 on the Nativity of the Lord