How did the Holy Spirit perform this “Immaculate Conception”?
Possibility #1: the Holy Spirit provided the male sperm necessary
Possibility #2: the Holy Spirit “created” the fetus in Mary’s womb
"The incarnation of Christ is a most extraordinary and amazing affair; it is wonderful indeed, that the eternal Son of God should become man; that he should be born of a pure virgin, without any concern of man in it; that this should be brought about by the power of the Holy Ghost, in a way unseen, imperceptible and unknown, signified by his overshadowing; and all this in order to effect the most wonderful work that ever was done in the world, the redemption and salvation of men: it is a most mysterious thing, incomprehensible by men, and not to be accounted for upon the principles of natural reason; and is only to be believed and embraced upon the credit of divine revelation, to which it solely belongs...."
"When the Virgin hesitated about what was told her by the angel, she was assured by him, that the Holy Ghost should come upon her, and the power of the Highest should overshadow her; and accordingly the birth of Christ was on this wise, when Joseph and Mary were espoused, before they came together, “she was found with child of the Holy Ghost;” and Joseph was told, in order to encourage him to take her to wife, that what was “conceived in her, was of the Holy Ghost;” and therefore he himself was not incarnate; (see
Luke 1:35;
Matthew 1:18,
20). It remains, that it is the second Person, the Son of God, who is meant by “the Word that was made flesh”, or became incarnate; and, indeed, it is explained of him in the same passage; for it follows; “And we beheld his glory, the glory as of the only begotten of the Father,” And it is easy to observe, that the same divine Person that bears the name of the Word, in the order of the Trinity, in one place, has that of the Son in another; by which it appears they are the same; (compare
1 John 5:7 with
Matthew 28:19)...."
“the Lord from heaven” (
1 Cor. 15:47). But the words are not to be understood of the descent of the human nature of Christ from heaven; but of his divine Person from thence; not by change of place, but by assumption of the human nature into union with him; by virtue of which union the man Christ has the name of the “Lord from heaven;” and not because of the original and descent of the human nature from thence; and in this sense, and in this sense only, are we to understand the words of Christ, when he says, “I came down from heaven” (
John 6:38), namely, that he descended in and by the human nature; not by bringing it down from thence, but by taking it into union with his divine Person.
2d1b. This conception was through the power and influence of the Holy Ghost, overshadowing the virgin. His operations in this affair may be considered in this manner, and after this order; He first took a part and portion of the virgin, of her semen, or blood, and conveyed it to a proper place; and purified and sanctified it, or separated it, not from any moral impurity, which it was not capable of, being an unformed mass; but from a natural indisposition in it, which, had it not been removed, might hereafter have occasioned sin; to prevent which this was done; and then he impregnated it with a fructifying virtue, and formed the members of the human body, in order, at once, and in a fitness (being properly organized) to receive the human soul; for to consider its immediate formation in such a state, is much more agreeable to the formation of the first man, more becoming the workmanship of the Holy Ghost, and more suitable to the dignity of the Son of God to assume it into union with himself, than to suppose it an unformed and unshapen embryo. Yet this is to be understood, not as if it was in such a state as not to admit of a future increase, both before and after birth; nor to contradict its continuance in the womb of the virgin the usual time of every man. Now though this affair has been spoken of as in various processes, yet must be understood as all instantaneously done by the almighty power of the Holy Spirit: in the same instant the human body was thus conceived, formed, and organized, the human soul of Christ was created and united to it, by him who “forms the spirit of man within him;” and in that very instant the body was conceived and formed, and the soul united to it, did the Son of God assume the whole human nature at once, and take it into union with his divine Person, and gave it a subsistence in it; so that the human nature of Christ never had a subsistence of itself; but from the moment of its conception, formation, and creation, it subsisted in the Person of the Son of God: and hence the human nature of Christ is not a person; a person is that which subsists of itself: but that the human nature of Christ never did; therefore,
2d1c. It was a nature, and not a person, that Christ assumed so early as at its conception; it is called “the holy Thing”, and not a person; “The seed of Abraham”, or the nature of the seed of Abraham; the “form” and “fashion” of a man, that is, the nature of man; as “the form of God”, in the same passage, signifies the nature of God; (see
Luke 1:35;
Heb. 2:16;
Phil. 2:6-8)."
From
John Gill: Doctrinal Divinity - Christian Classics Ethereal Library