4 Having then mentioned all His forefathers, and ending with Joseph, he did not stop at this, but added, “Joseph the husband of Mary;” intimating that it was for her sake he traced his genealogy also. Then, lest when you have heard of the “husband of Mary,” you should suppose that Christ was born after the common law of nature, mark, how he sets it right by that which follows. “You have heard,” says he, “of an husband, you have heard of a mother, you have heard a name assigned to the child, therefore hear the manner too of the birth.” “The birth of Jesus Christ was on this wise.” “Of what kind of birth are you telling me, I pray you, since you have already mentioned His ancestors?” “I still wish to tell you the manner also of His birth.” Do you see, how he wakens up the hearer? For as though he were about to speak of something unusual, he promises to tell also the manner thereof.
And observe a most admirable order in the things he has mentioned. For he did not proceed directly to the birth, but puts us in mind first, how many generations he was from Abraham, how many from David, and from the captivity of Babylon; and thus he sets the careful hearer upon considering the times, to show that this is the Christ who was preached by the prophets. For when you have numbered the generations, and hast learned by the time that this is He, you will readily receive likewise the miracle which took place in His birth. Thus, being about to tell of a certain great thing, His birth of a virgin, he first shadows over the statement, until he has numbered the generations, by speaking of “an husband of Mary;” or rather he does even put in short space the narration of the birth itself, and then proceeds to number also the years, reminding the hearer, that this is He, of whom the patriarch Jacob had said, He should then at length come, when the Jewish rulers had come to an end; of whom the prophet Daniel had proclaimed beforehand, that He should come after those many weeks. And if any one, counting the years spoken of to Daniel by the angel in a number of weeks, would trace down the time from the building of the city to His birth, by reckoning he will perceive the one to agree with the other.
Source: Homilies on the Gospel of St. Matthew (New Advent)