3 Hearing these things, arise, and surmise nothing low: but even because of this very thing most of all should you marvel, that being Son of the Unoriginate God, and His true Son, He suffered Himself to be called also Son of David, that He might make you Son of God. He suffered a slave to be father to Him, that He might make the Lord Father to you a slave.
Do you see at once from the beginning of what nature are the Gospels? If you doubt concerning the things that pertain to you, from what belongs to Him believe these also. For it is far more difficult, judging by human reason, for God to become man, than for a man to be declared a Son of God. When therefore you are told that the Son of God is Son of David and of Abraham, doubt not any more that thou too, the son of Adam, shall be son of God. For not at random, nor in vain did He abase Himself so greatly, only He was minded to exalt us. Thus He was born after the flesh, that you might be born after the Spirit; He was born of a woman, that you might cease to be the son of a woman.
Wherefore the birth was twofold, both made like us, and also surpassing ours. For to be born of a woman indeed was our lot, but “to be born not of blood, nor of the will of flesh, nor of man,” but of the Holy Ghost, was to proclaim beforehand the birth surpassing us, the birth to come, which He was about freely to give us of the Spirit. And everything else too was like this. Thus His baptism also was of the same kind, for it partook of the old, and it partook also of the new. To be baptized by the prophet marked the old, but the coming down of the Spirit shadowed out the new. And like as though any one were to place himself in the space between any two persons that were standing apart, and stretching forth both his hands were to lay hold on either side, and tie them together; even so has He done, joining the old covenant with the new, God's nature with man's, the things that are His with ours.
Do you see the flashing brightness of the city, with how great a splendor it has dazzled you from the very beginning? How it has straightway shown the King in your own form; as though in a camp? For neither there does the king always appear bearing his proper dignity, but laying aside the purple and the diadem, he often disguises himself in the garb of a common soldier. But there it is, lest by being known he should draw the enemy upon himself; but here on the contrary, lest, if He were known, He should cause the enemy to fly from the conflict with Him, and lest He should confound all His own people: for His purpose was to save, not to dismay.
Source: Homilies on the Gospel of St. Matthew (New Advent)