He describes the person giving birth: first, from her condition, secondly, from her dignity; thirdly from her name.
He says, therefore, When his mother Mary had been betrothed to Joseph . But immediately a question arises. Since Christ willed to be born of a virgin, why should he want his mother to be betrothed? According to Jerome there are three reasons: the first is that the testimony to her virginity be more credible. For if she had not been betrothed and said that she is a virgin, when she was pregnant, it would seem that she claimed to be a virgin merely to conceal the crime of adultery. But there was no need to lie, when she was betrothed. And therefore, there was more reason to believe her: "Your testimonies were made exceedingly credible" (Ps 119:144). Another reason is that she would have the protection of a man, both when she fled into Egypt and when she returned. The third reason was in order that her offspring would be concealed from the devil; otherwise, if he knew, he would impede his passion and the fruit of our redemption: "If they had known, they would never have crucified the Lord of glory" (1 Cor 2:8). This is explained of the devil, i.e., not to permit him to be crucified.
But on the other hand, could not the devil know whether she was a virgin? For her virginity was in inviolate flesh. Therefore, the devil could know that she was a virgin. The answer is, according to Ambrose, who also assigns this reason: namely, that devils are by the subtlety of their nature capable of things which they cannot do without God's permission. Hence the devil would have known her virginity, if God had not prevented him from making a careful examination. According to Ambrose, there are three reasons for this:
the first is to preserve the honor of the mother of God: "The Lord preferred that men wonder about his origin, rather than about his mother's purity. Therefore, he willed that she be espoused, in order that any suspicion of adultery be removed; for he had come to fulfill the Law, not to destroy it: "I have come not to destroy the law but to fulfill it" (Mt 5:17); "Honor your father and your mother" (Ex 20:12).
Another reason is so that virgins observed in adultery might have no excuse; for if the Lord's mother had not been betrothed and yet pregnant, others could excuse themselves through her: "Incline not my heart to any evil to busy myself with wicked deeds" (Ps 141:4).
The third reason is because Christ espoused the Church to himself, and it is a virgin: "I have betrothed you to Christ" (2 Cor 11:2). Consequently, he willed to be born of a betrothed virgin as a sign that he had betrothed the Church to himself.
When his mother Mary had been betrothed . But to whom? To Joseph . According to Chrysostom, Joseph was a wood-worker and he signifies Christ, who restored all things through the wood of the cross in heaven and on the earth.
His mother , i.e., of God. Here is shown her dignity: for it has been granted to no creature, no man, no angel, to be the father or mother of God. But this was a privilege of a singular grace that she become the mother not only of a man but of God. Therefore, it says in Rev (12:1): "A woman clothed with the sun," as though filled with the Holy Trinity. Nestorius denied this, because the divinity was not received from the virgin. Against this the martyr Ignatius uses a beautiful example to show that she was the mother of God. "It is obvious," he says, "that in the generation of men in general the woman is called the mother; yet the woman does not give the rational soul, which is from God, but she gives the substance for the formation of the body. But the woman is called the mother of the whole man, because that which was taken from her is united to the rational soul. Similarly, since the humanity of Christ was taken from the Blessed Virgin, then on account of its being united to the divinity, the Blessed Virgin is called not only the mother of a man but also of God; although the divinity was not received from her any more than the rational soul in other is obtained from the mother.
Mary , a proper name is taken to mean star of the sea or enlightener and lady; hence in Rev (12:1) she is described with the moon under her feet.
Before they came together... Here Elvidius objects: "If before they came together, then at some time they did come together." Hence, he denied the virginity of Christ's mother: not before birth, not during the birth, but after the birth, he says that she was known by her husband. Jerome answers that no doubt the word "before" always implies a relationship to the future. But his can be in two ways: either according to reason or according to the acceptation of the intellect. For if one says: "Before I ate in the port at Rome, I sailed to Africa," that does not mean that after I sailed to Africa, I ate; but that I had intended to eat and, prevented by the sailing, I did not eat. And that is the case here. It should not be interpreted in such a way that later they really came together, as that knave says, but because from the very fact that she was betrothed to him according to general opinion, it was lawful for them to come together, although they never did.
Remigius explains it another way, so that it is understood of the solemn celebration of marriage: the betrothal occurred and took place for some days, and in the meantime the spouse was not under the husband's care. Later the solemn celebration of the marriage took place, and then the wife was brought to the husband's house. It is about this marriage ceremony that the evangelist is speaking here. Accordingly, Elvidius' objection has no place.
She was found... Note the appropriateness of the word. For, properly speaking, that is said to be found, concerning which there was no thought or hope; and Joseph had such an opinion of Mary's purity, that it was beyond his expectation to find her pregnant.
Found to be with child . Found by Joseph who, as Jerome says, in virtue of the marriage searched out all her secrets.
Of the Holy Spirit . Here he touches on the cause of the conception. This must be read separately from the preceding phrase. For it should not be read or understood that Joseph found her with child of the Holy Spirit, but merely that he found her pregnant. But in order that no suspicion of adultery arise in the mind of the hearers, he added of the Holy Spirit , i.e. from the power of the Holy Spirit not from his substance, lest he be regarded the son of the Holy Spirit: "The Holy Spirit will come upon you, and the power of the Most High shall overshadow you" (Lk 1:35).
But although, according to Augustine, the works of the Trinity are indivisible, so that not only the Holy Spirit but also the Father and Son produced this conception; yet by a certain appropriateness it is attributed to the Holy Spirit. There are three reasons for this:
the first is that the Holy Spirit is love. But this is the greatest sign of live, that God will his Son to be incarnate: "God so loved the world that he gave his only begotten Son" (Jn 3:16).
Secondly, because grace is attributed to the Holy Spirit: "There are varieties of graces but the same Spirit" (1 Cor 12:4).
The third reason is assigned in the deliberations of the Council of Nicea, namely, that there are two words in us: the word of the heart and the word of the voice. The heart's word is the intellect's conception, which is hidden from men, except in so far as it is uttered by the voice or by a word of the voice. To the word of the heart is compared the eternal Word before the incarnation, when he was with the Father and hidden from us; but to the voice's word is compared the incarnate Word, which has already appeared to us and has been manifested. But the heart's word is not joined to the voice save through the spirit; and therefore, it was correct to say that the incarnation of the Word, through which he appeared visible to us was made through the medium of the Holy Spirit.
Note here four reasons why Christ willed to be born of a virgin:
first, because original sin is contracted in the offspring from the union of man and woman; hence, if Christ had been born of a marriage act, he would have contracted original sin. But this would be unbecoming, since he had come into the world to take away our sins. Hence, he ought not have been infected with the contagion of sin.
The second is that Christ was the principal teacher of chastity: "There are eunuchs who have made themselves eunuchs for the sake of the kingdom of heaven" (Mt 19:12).
The third is on account of purity and cleanness: "Wisdom will not enter into a sinful soul" (Wis 1:4). Hence, it was fitting that his mother's womb not be defiled with any corruption.
The fourth is on account of a property of a word: because as a word emanates from the heart, so Christ willed and should have been born from the Virgin without any defilement.
(19) Her husband Joseph being a just man . After indicating the manner of the generation, he now confirms it with witnesses. For when he had said above that the mother of Jesus was found with child and that this was of the Holy Spirit, someone might believe that the evangelist mentioned this out of respect for the Master. Therefore, the evangelist now confirms the aforesaid manner of generation: first, by a prophetic pronouncement: "All this took place..." (v. 22); secondly, the person revealing: "But as he considered this..." (v. 20); thirdly, the words of the revelation are presented: "Joseph, son of David..." (v. 20b).
The person to whom the revelation is made is commended for two things, namely, that he is just and, therefore, did not lie; secondly, from the fact that he was her spouse or husband and, therefore, would not tolerate any crime in her: "The zeal and fury of the husband will not spare, when he takes revenge" (Pr 6:34).