Saint Gabriel did not say “what is born to thee” but “what is born of thee”

The Verb takes hold of the seed of Abraham, as the apostle said; whence it behoved Him to be made like His brethren in all things, and to take a Body like us. This is why Mary is truly presupposed, in order that He may take it from her, and offer it for us as His own. And this Isaiah pointed to in his prophecy, in the words: ‘Behold the Virgin, while Gabriel is sent to her—not simply to a virgin, but to a virgin betrothed to a man, in order that by means of the betrothed man he might shew that Mary was really a human being.’ And for this reason Scripture also mentions her bringing forth, and tells of her wrapping Him in swaddling clothes; and therefore, too, the paps which He sucked were called blessed. And He was offered as a sacrifice, in that He Who was born had opened the womb. Now all these things are proofs that the Virgin brought forth.

And Gabriel preached the Gospel to her without uncertainty, saying not merely ‘what is born in thee,’ lest the body should be thought to be extraneously induced upon her, but ‘of thee,’ that what was born might be believed to be naturally from her, inasmuch as Nature clearly shews that it is impossible for a virgin to produce milk unless she has brought forth, and impossible for a body to be nourished with milk and wrapped in swaddling clothes unless it has previously been naturally brought forth. …This He did, and so it was, in order that Himself taking what was ours and offering it as a sacrifice, He might do away with it, and conversely might invest us with what was His, and cause the Apostle to say: ‘This corruptible must put on incorruption, and this mortal put on immortality.’

… Now this did not come to pass putatively, as some have supposed—far be the thought—but the Savior having in very truth become Man, the salvation of the whole man was brought about... Truly our salvation is not merely apparent, nor does it extend to the body only, but the whole man, body and soul alike, has truly obtained salvation in the Word Himself. That then which was born of Mary was according to the divine Scriptures human by nature, and the Body of the Lord was a true one—but it was this—because it was the same as our body, for Mary was our sister inasmuch as we all are from Adam.

Saint Athanasius

Letter to Epictetus, bishop of Corinth