2 But what is this vestibule? “The book of the generation of Jesus Christ, Son of David, Son of Abraham.”
“What do you say? Did you not promise to discourse of the Only-begotten Son of God, and do you make mention of David, a man born after a thousand generations, and say that he is both father and ancestor?” Stay, seek not to learn all at once, but gently and little by little. Why, it is in the vestibule that you are standing, by the very porch; why then do you hasten towards the inner shrine? As yet you have not well marked all without. For neither for a while do I declare unto you that other generation: or rather not even this which comes after, for it is unutterable, and unspeakable. And before me the Prophet Esaias has told you this; where when proclaiming His passion, and His great care for the world, and admiring who He was, and what He became, and whither He descended, he cried out loud and clear, saying thus, “Who shall declare His generation?”
It is not then of that we are now to speak, but of this beneath, this which took place on earth, which was among ten thousand witnesses. And concerning this again we will relate in such wise as it may be possible for us, having received the grace of the Spirit. For not even this may any one set forth altogether plainly, forasmuch as this too is most awful. Think not, therefore, it is of small things you are hearing, when you hear of this birth, but rouse up your mind, and straightway tremble, being told that God has come upon earth. For so marvellous was this, and beyond expectation, that because of these things the very angels formed a choir, and in behalf of the world offered up their praise for them, and the prophets from the first were amazed at this, that “He was seen upon earth, and conversed with men.” Yea, for it is far beyond all thought to hear that God the Unspeakable, the Unutterable, the Incomprehensible, and He that is equal to the Father, has passed through a virgin's womb, and has vouchsafed to be born of a woman, and to have Abraham and David for forefathers. But why do I say Abraham and David? For what is even more amazing, there are those women, whom we have lately mentioned.
Source: Homilies on the Gospel of St. Matthew (New Advent)