Homily 1 on Matthewhttp://www.newadvent.org/fathers/200101.htm
14. And this because the questions are many and frequent. See, for instance, at once in the beginning of his Gospel, how many difficulties might be raised one after the other. As first, wherefore the genealogy of Joseph is traced, who was not father of Christ. Secondly, whence may it be made manifest that He derives His origin from David, while the forefathers of Mary, who bare Him, are not known, for the Virgin's genealogy is not traced? Thirdly, on what account Joseph's genealogy is traced, when he had nothing to do with the birth; while with regard to the Virgin, who was the very mother, it is not shown of what fathers, or grandfathers, or ancestors, she is sprung.
Homily 2 on Matthewhttp://www.newadvent.org/fathers/200102.htm
7. "But whence is it manifest that He is of David?" one may say. For if He was not sprung of a man, but from a woman only, and the Virgin has not her genealogy traced, how shall we know that He was of David's race? Thus, there are two things inquired; both why His mother's genealogy is not recited, and wherefore it can be that Joseph is mentioned by them, who has no part in the birth: since the latter seems to be superfluous, and the former a defect.
Of which then is it necessary to speak first? How the Virgin is of David. How then shall we know that she is of David? Hearken unto God, telling Gabriel to go unto "a virgin betrothed to a man (whose name was Joseph), of the house and lineage of David." What now would you have plainer than this, when you have heard that the Virgin was of the house and lineage of David?
Hence it is evident that Joseph also was of the same. Yes, for there was a law, which bade that it should not be lawful to take a wife from any other stock, but from the same tribe. And the patriarch Jacob also foretold that He should arise out of the tribe of Judah, saying on this wise: "there shall not fail a ruler out of Judah, nor a governor out of his loins, until He come for whom it is appointed, and He is the expectation of the Gentiles."
"Well; this prophecy does indeed make it clear that He was of the tribe of Judah, but not also that He was of the family of David. Was there then in the tribe of Judah one family only, even that of David, or were there not also many others? And might it not happen for one to be of the tribe of Judah, but not also of the family of David?"Nay, lest you should say this, the evangelist has removed this suspicion of yours, by saying, that He was "of the house and lineage of David."
And if you wish to learn this from another reason besides, neither shall we be at a loss for another proof. For not only was it not allowed to take a wife out of another tribe, but not even from another lineage, that is, from another kindred. So that if either we connect with the Virgin the words, "of the house and lineage of David," what has been said stands good; or if with Joseph, by that fact this also is proved. For if Joseph was of the house and lineage of David, he would not have taken his wife from another than that whence he himself was sprung."What then," one may say, "if he transgressed the law?" Why, for this cause he has by anticipation testified that Joseph was righteous, on purpose that you might not say this, but having been told his virtue, might be sure also that he would not have transgressed the law. For he who was so benevolent, and free from passion, as not to wish, even when urged by suspicion, to attempt inflicting punishment on the Virgin, how should he have transgressed the law for lust? He that showed wisdom and self-restraint beyond the law (for to put her away, and that privily, was to act with self-restraint beyond the law), how should he have done anything contrary to the law; and this when there was no cause to urge him?
8. Now that the Virgin was of the race of David is indeed from these things evident; but wherefore he gave not her genealogy, but Joseph's, requires explanation. For what cause was it then? It was not the law among the Jews that the genealogy of women should be traced. In order then that he might keep the custom, and not seem to be making alterations from the beginning, and yet might make the Virgin known to us, for this cause he has passed over her ancestors in silence, and traced the genealogy of Joseph. For if he had done this with respect to the Virgin, he would have seemed to be introducing novelties; and if he had passed over Joseph in silence, we should not have known the Virgin's forefathers. In order therefore that we might learn, touching Mary, who she was, and of what origin, and that the laws might remain undisturbed, he has traced the genealogy of her espoused husband, and shown him to be of the house of David. For when this has been clearly proved, that other fact is demonstrated with it, namely, that the Virgin likewise is sprung from thence, by reason that this righteous man, even as I have already said, would not have endured to take a wife from another race.
There is also another reason, which one might mention, of a more mystical nature, because of which the Virgin's forefathers were passed over in silence; but this it were not seasonable now to declare, because so much has been already said.
Homily 3 on Matthewhttp://www.newadvent.org/fathers/200103.htm
(. . .)
Come, then, let us speak today what remains. What is it then that is now required? Why Joseph's genealogy is traced, who had no part in the birth. And one cause we have mentioned already; but it is necessary to mention likewise the other, that which is more mystical and secret than the first. What then is this? He would not that it should be manifest to the Jews, at the time of the birth, that Christ was born of a virgin.
(. . .)
It is then for this reason that both Joseph has his genealogy traced, and the Virgin betrothed to him. For if even he, who was both a just and wondrous man, required many things, in order that he should receive that which had come to pass; an angel, and the vision in dreams, and the testimony from the prophets; how could the Jews, being both dull and depraved, and of so unfriendly spirit towards Him, have admitted this idea into their minds? For the strangeness and novelty thereof would be sure greatly to disturb them, and the fact that they had never so much as heard of such a thing having happened in the times of their forefathers. For as the man who was once persuaded that He is Son of God, would after that have no cause to doubt concerning this too; so he who was accounting Him to be a deceiver and an adversary of God, how could he but have been yet more offended by this, and have been led on unto the opposite notion? For this cause neither do the apostles at the first directly say this, but while of His resurrection they discourse much and often (forasmuch as of this there were examples in the times before, although not such as this); that He was born of a virgin they do not say always: nay, not even His mother herself ventured to utter this. See, for instance, what says the Virgin even to Himself: "Behold, Your father and I have sought You." Luke 2:48 For if this suspicion had been entertained, neither would He any longer have been accounted to be a Son of David, and this opinion not being held, many other evils besides would have arisen. For this cause neither do the angels say these things to all, but to Mary only, and Joseph; but when showing to the shepherds the glad tidings of that which had come to pass, they no longer added this.
2 Corinthians 4:3-4
And if our gospel be also hid, it is hid to them that are lost, In whom the god of this world hath blinded the minds of unbelievers, that the light of the gospel of the glory of Christ, who is the image of God, should not shine unto them.