28 And let not the law of adoption seem to you to be foreign to our Scriptures, and that, as if it were recognised only in the practice of human laws, it cannot fall in with the authority of the divine books. For it is a thing established of old time, and frequently heard of in the Ecclesiastical books — that not only the natural way of birth, but the free choice of the will also, should give birth to a child. For women, if they had no children of their own, used to adopt children born of their husbands by their hand-maids, and even oblige their husbands to give them children in this way; as Sarah, Rachel, and Leah. And in doing this the husbands did not commit adultery, in that they obeyed their wives in that matter which had regard to conjugal duty, according to what the Apostle says: “The wife has not power of her own body, but the husband; and likewise also the husband has not power of his own body, but the wife.” Moses too, who was born of a Hebrew mother and was exposed, was adopted by Pharaoh's daughter. There were not then indeed the same forms of law as now, but the choice of the will was taken for the rule of law, as the Apostle says also in another place, “The Gentiles which have not the law, do by nature the things contained in the law.” But if it is permitted to women to make those their children to whom they have not given birth, why should it not be allowed men to do so too with those whom they have not begotten of their body, but of the love of adoption. For we read that the patriarch Jacob even, the father of so many children, made his grandchildren, the sons of Joseph, his own children, in these words: “These too shall be mine, and they shall receive the land with their brethren, and those which you beget after them shall be yours.” But it will be said, perhaps, that this word “adoption” is not found in the Holy Scriptures. As though it were of any importance by what name it is called, when the thing itself is there— for a woman to have a child to whom she has not given birth, or a man a child whom he has not begotten. And he may, without any opposition from me, refuse to call Joseph adopted, provided he grant that he may have been the son of a man of whose body he was not born. Yet the Apostle Paul does continually use this very word “adoption,” and that to express a great mystery. For though Scripture testifies that our Lord Jesus Christ is the only Son of God, it says, that the brethren and coheirs whom He has vouchsafed to have, are made so by a kind of adoption through Divine grace. “When,” says he, “the fullness of time had come, God sent forth His Son, made of a woman, made under the law, to redeem them that were under the law, that we might receive the adoption of sons.” And in another place: “We groan within ourselves, waiting for the adoption, to wit, the redemption of our body.” And again, when he was speaking of the Jews, “I could wish that myself were accursed from Christ for my brethren, my kinsmen according to the flesh; who are Israelites, to whom pertains the adoption, and the glory, and the testaments, and the giving of the law; whose are the fathers, and of whom as concerning the flesh Christ came, Who is over all, God blessed for ever.” Where he shows, that the word “adoption,” or at least the thing which it signifies, was of ancient use among the Jews, just as was the Testament and the giving of the Law, which he mentions together with it.
Source: Sermons on Selected Lessons of the New Testament (New Advent)