Luke 1:34

A heavenly fire engenders him, not flesh Nor blood of father, nor impure desire. By power of God a spotless maid conceives, As in her virgin womb the Spirit breathes. The mystery of this birth confirms our faith That Christ is God: a maiden by …

Her virginity also itself was on this account more pleasing and accepted, in that it was not that Christ being conceived in her, rescued it beforehand from a husband who would violate it, Himself to preserve it; but, before He was conceived, chose it, already dedicated to God, as that from which to be born. This is shown by the words which Mary spoke in answer to the Angel announcing to her her conception; "How," says she, "shall this be, seeing I know not a man?" Which assuredly she would not say, unless she had before vowed herself unto God as a virgin. But, because the habits of the Israelites as yet refused this, she was espoused to a just man, who would not take from her by violence, but rather guard against violent persons, what she had already vowed. Although, even if she had said this only, "How shall this take place?" and had not added, "seeing I know not a man," certainly she would not have asked, how, being a female, she should give birth to her promised Son, if she had married with purpose of sexual intercourse. She might have been bidden also to continue a virgin, that in her by fitting miracle the Son of God should receive the form of a servant, but, being to be a pattern to holy virgins, lest it should be thought that she alone needed to be a virgin, who had obtained to conceive a child even without sexual intercourse, she dedicated her virginity to God, when as yet she knew not what she should conceive, in order that the imitation of a heavenly life in an earthly and mortal body should take place of vow, not of command; through love of choosing, not through necessity of doing service. Thus Christ by being born of a virgin, who, before she knew Who was to be born of her, had determined to continue a virgin, chose rather to approve, than to command, holy virginity. […]

The first sinner, the first transgressor, begot sinners liable to death. To heal them, the Savior came from the Virgin; because he didn't come to you the way you came, seeing that he did not originate from the sexual appetite of male and female, not from that chain of lust. The Holy Spirit, it says, will come upon you. That was said to the Virgin glowing with faith, not seething with carnal lust. The Holy Spirit will come upon you, and the power of the Most High will overshadow you [Luke 1:35]. Being overshadowed like that, how could she be seething with the heat of sexual desire? So, because he didn't come to you the way you came, he sets you free.

(Orat. in Diem Nat. Christi.) Hear the chaste words of the Virgin. The Angel tells her she shall bear a son, but she rests upon her virginity, deeming her inviolability a more precious thing than the Angel's declaration. Hence she says, Seeing that I know not a man. (sup.) These words of Mary are a token of what she was pondering in the secrets of her heart; for if for the sake of the marriage union she had wished to be espoused to Joseph, why was she seized with astonishment when the conception was made known unto her? seeing in truth she might herself be expecting at the time to become a mother according to the law of nature. But because it was meet that her body being presented to God as an holy offering-should be kept inviolate, therefore she says, Seeing that I know not a man. As if she said, Notwithstanding that thou who speakest art an Angel, yet that I should know a man is plainly an impossible thing. How then can I be a mother, having no husband? For Joseph I have acknowledged as my betrothed. (Orat. in Diem Nat.) O blessed is that womb which because of the overflowing purity of the Virgin Mary has drawn to itself the gift of life! For in others scarcely indeed shall a pure soul obtain the presence of the Holy Spirit, but in her the flesh is made the receptacle of the Spirit. (Lib. de Vita Moysis.) For the tables of our nature which guilt had broken, the true Lawgiver has formed anew to Himself from our dust without cohabitation, creating a body capable of taking His divinity, which the finger of God hath carved, that is to say, the Spirit coming upon the Virgin. (in Diem Natal.) Moreover, the power of the Highest shall overshadow thee. Christ is the power of the most high King, who by the coming of the Holy Spirit is formed in the Virgin. (Orat. […]

Then the virgin was initiated into the mystery by Gabriel. The words of the mystagogy were a blessing. "Hail," he says, "blessed woman, the Lord is with you." [...] He says, "You will conceive in your womb and will bear a son and you shall call his name 'Jesus'." [Luke 1:31, Protevangelium of James 11.3] And what did Mary do? Listen to the pure virgin's utterance. The angel declared the birth, and she clings to her virginity, judging incorruption to be nobler than the angelic appearance and could neither disbelieve the angel nor abandon her judgments. She says, I have no experience of intercourse with a husband: "How will this happen to me, since I have not known a husband?" [Luke 1:34] Mary's very utterance is proof of what is narrated in the apocryphal book [the Protevangelium of James]. For if she had been taken by Joseph for marriage, how could she be totally astonished at the one who announced the birth to her if she was quite favorably disposed to becoming a mother according to the law of nature? But since the flesh that had been consecrated to God had to be kept inviolate like one of the holy dedicated things, this is why she says, "Even if you are an angel, even if you have come from heaven, even if the appearance was beyond humanity, still for a husband to know me is not possible. How will I become a mother without a husband? I know Joseph as a fiancé, but I have not known a husband." And what did Gabriel (the bridal escort) do? What sort of bridal chamber did he announce for the pure and undefiled marriage? "The Holy Spirit," he says, "will come upon you and the power of the Most High will overshadow you." [Luke 1:35, Protevangelium of James 11.3]

It was fitting that the Architect of the works of creation should come and raise up the house that had fallen and that the hovering Spirit should sanctify the buildings that were unclean. Thus, if the Progenitor entrusted the judgment that is to come to …

But the birth of our Lord Jesus Christ exceeds all understanding and goes beyond any precedent.

Each one is a partaker of this spiritual origin in regeneration. To every one, when he is reborn, the water of baptism is like the Virgin's womb, for the same Holy Spirit fills the font, who filled the Virgin, that the sin, which that sacred conception overthrew, may be taken away by this mystical washing.

In this nativity also, Isaiah's saying is fulfilled, "let the earth produce and bring forth salvation, and let righteousness spring up together." [Isaiah 45:8] For the earth of human flesh, which in the first transgressor, was cursed, in this Offspring of the Blessed Virgin only produced a seed that was blessed and free from the fault of its stock. And each one is a partaker of this spiritual origin in regeneration; and to every one when he is re-born, the water of baptism is like the Virgin's womb; for the same Holy Spirit fills the font, Who filled the Virgin, that the sin, which that sacred conception overthrew, may be taken away by this mystical washing.

(235. Ep. Amph.) Knowledge is spoken of in various ways. The wisdom of our Creator is called knowledge, and an acquaintance with His mighty works, the keeping also of His commandments, and the constant drawing near to Him; and besides these the marriage union is called knowledge, as it is here. (Lib. de Spirit. Sanct. c. v.) Hence also, St. Paul says, God sent forth his Son, born not (through a woman) but of a woman. For the words through a woman might convey only a notion of birth as a passing through, but when it is said, of a woman, (Gal. 4:4.) there is openly declared a communion of nature between the son and the parent.

And hear again how Isaiah in express words foretold that He should be born of a virgin; for he spoke thus: "Behold, a virgin shall conceive, and bring forth a son, and they shall say for His name, `God with us.'" For things which were incredible and seemed impossible with men, these God predicted by the Spirit of prophecy as about to come to pass, in order that, when they came to pass, there might be no unbelief, but faith, because of their prediction. But lest some, not understanding the prophecy now cited, should charge us with the very things we have been laying to the charge of the poets who say that Jupiter went in to women through lust, let us try to explain the words. This, then, "Behold, a virgin shall conceive," signifies that a virgin should conceive without intercourse. For if she had had intercourse with any one whatever, she was no longer a virgin; but the power of God having come upon the virgin, overshadowed her, and caused her while yet a virgin to conceive. And the angel of God who was sent to the same virgin at that time brought her good news, saying, "Behold, thou shalt conceive of the Holy Ghost, and shalt bear a Son, and He shall be called the Son of the Highest, and thou shalt call His name Jesus; for He shall save His people from their sins," -as they who have recorded all that concerns our Saviour Jesus Christ have taught, whom we believed, since by Isaiah also, whom we have now adduced, the Spirit of prophecy declared that He should be born as we intimated before. It is wrong, therefore, to understand the Spirit and the power of God as anything else than the Word, who is also the first-born of God, as the foresaid prophet Moses declared; and it was this which, when it came upon the virgin and overshadowed her, caused her to conceive, not by intercourse, but by power. […]

(Hom. 49 in Gen.) As if he said, Look not for the order of nature in things which transcend and overpower nature. Dost thou say, How shall this be, seeing I know not a man? Nay rather, shall it happen to thee for this very reason, that thou hast never known a husband. For if thou hadst, thou wouldest not have been thought worthy of the mystery, not that marriage is unholy, but virginity more excellent. It became the common Lord of all both to take part with us, and to differ with us in His nativity; for the being born from the womb, He shared in common with us, but in that He was born without cohabitation, He was exalted far above us.

The Virgin said, "How will this be?" not because she disbelieved, but because she, being wise and understanding, wished to learn the manner of the present event, for nothing like it had ever happened before, nor would it happen after. Therefore the Angel pardons Her …

But Mary said to the Angel. The Evangelist first introduced the Angel narrating; here he adds the most prudent Virgin inquiring: in which inquiry three things are explained to us, namely, a fitting doubt, a moving reason, and a satisfying solution. — A fitting doubt …

Thus animated to cast out fear by a spirit of faith, she said to the angel: "How shall this be done, for I know not man?" She doubts not the fact, but only inquires about the manner of its accomplishment. She says not "Will it …

Theotokos: Make plain to me, how I, a virgin, shall bear him? The angel: You seek to know from me the manner of your conceiving, Virgin, but this is beyond all interpretation! The Holy Spirit will overshadow you in his creative power and shall make …

(18 Moral. c. 20. super Job 27:21.) By the term overshadowing, both natures of the Incarnate God are signified. For shadow is formed by light and matter. But the Lord by His Divine nature is light. Because then immaterial light was to be embodied in the Virgin's womb, it is well said unto her, The power of the Highest shall overshadow thee, that is, the human body in thee shall receive an immaterial light of divinity. For this is said to Mary for the heavenly refreshing of her soul. (18 Moral. c. 52. super Job 28:19.) To distinguish His holiness from ours, Jesus is stated in an especial manner to be born holy. For we although indeed made holy, are not born so, for we are constrained by the very condition of our corruptible nature to cry out with the Prophet, Behold, I was conceived in iniquity. (Ps. 51:5.) But He alone is in truth holy, who was not conceived by the cementing of a fleshly union, nor as the heretics rave, one person in His human nature, another in His divine; not conceived and brought forth a mere man, and afterwards by his merits, obtained that He should be God, but the Angel announcing and the Spirit coming, first the Word in the womb, afterwards within the womb the Word made flesh. Whence it follows, Shall be called the Son of God.

(Geometer.) But mark, how the Angel solves the Virgin's doubts, and shows to her the unstained marriage and the unspeakable birth. And the Angel answered, and said unto her, The Holy Spirit shall come upon thee. (Victor Presbyter.) But observe, how the Angel has declared the whole Trinity to the Virgin, making mention of the Holy Spirit, the Power, and the Most High, for the Trinity is indivisible.c

Let Nestorius then cease to say that the Virgin's Son is only man, and to deny that He is taken up by the Word of God into the unity of the Person. For the Angel when he says that the very same has David for His father whom he declares is called the Son of the Highest, demonstrates the one Person of Christ in two natures. The Angel uses the future tense  (vocabitur, regnabit) not because, as the Heretics say, Christ was not before Mary, but because in the same person, man with God shares the same name of Son. Thou shalt conceive then not by the seed of man whom thou knowest not, but by the operation of the Holy Spirit, with which thou art filled. There shall be no flame of desire in thee when the Holy Spirit shall overshadow thee.

But Mary said to the angel: How will this be, since I do not know a man? She reverently expressed the purpose of her mind, that is, that she had decided to lead a virginal life. Because she was the first among women to devote …

Article 4. Whether the Mother of God took a vow of virginity? Objection 1. It would seem that the Mother of God did not take a vow of virginity. For it is written (Deuteronomy 7:14): "No one shall be barren among you of either sex." …

Then said Mary to the angel, how shall this be,....

The interview between Mary the mother of Jesus and Elisabeth the mother of John, when they were both with child of those pregnant births, and the prophecies they both uttered upon that occasion,

How, &c.--not the unbelief of Zacharias, "Whereby shall I know this?" but, taking the fact for granted, "How is it to be, so contrary to the unbroken law of human birth?" Instead of reproof, therefore, her question is answered in mysterious detail.

Let us mark, in these verses — the reverent and discreet manner in which the angel Gabriel speaks of the great mystery of Christ's incarnation. In reply to the question of Mary, "How shall this be?" he uses these remarkable words, "The Holy Spirit shall come upon you — and the power of the Highest shall overshadow you." We shall do well to follow the example of the angel in all our reflections on this deep subject.

Let us mark, in these verses — the reverent and discreet manner in which the angel Gabriel speaks of the great mystery of Christ's incarnation. In reply to the question of Mary, "How shall this be?" he uses these remarkable words, "The Holy Spirit shall come upon you — and the power of the Highest shall overshadow you." We shall do well to follow the example of the angel in all our reflections on this deep subject. Let us ever regard it with holy reverence — and abstain from those improper and unprofitable speculations upon it, in which some have unhappily indulged. It is enough for us to know that "the Word was made flesh," and that when the Son of God came into the world, he had a real body — so that He "took part of our flesh and blood," and was "made of a woman." Here we must stop. The manner in which all this was effected, is wisely hidden from us. If we attempt to pry beyond this point — we shall only darken counsel by words without knowledge, and rush in where angels fear to tread. In a religion which really comes down from Heaven — there must needs be mysteries. Of such mysteries in Christianity, the incarnation is one. Let us mark, in the second place — the prominent place assigned to the Holy Spirit in the great mystery of the incarnation. We find it written, "The Holy Spirit shall come upon you." An intelligent reader of the Bible will probably not fail to remember that the honor here given to the Spirit, is in precise harmony with the teaching of Scripture in other places. In every step of the great work of man's redemption — we shall find special mention of the work of the Holy Spirit. Did Jesus die to make atonement for our sins? It is written that "through the eternal Spirit, He offered himself without spot to God." (Hebrews 9:14.) Did Jesus rise again for our justification? It is written that He "was quickened by the Spirit."

Seeing I know not a man - Or, husband. As she was only contracted to Joseph, and not as yet married, she knew that this conception could not have yet taken place; and she modestly inquires by what means the promise of the angel is to be fulfilled in order to regulate her conduct accordingly.