30 And the angel said to her: Fear not, Mary, for thou hast found grace with God. 31 Behold thou shalt conceive in thy womb, and shalt bring forth a son; and thou shalt call his name Jesus.
Greek Expositor: The Virgin found favor with God, in that decking her own soul in the bright robes of chastity, she prepared a dwelling-place pleasing to God. Not only did she retain her virginity inviolate, but her conscience also she kept from stain. As many had found favor before Mary, he goes on to state what was peculiar to her. Behold, thou shalt conceive in thy womb.
By the word behold, he denotes rapidity and actual presence, implying that with the utterance of the word the conception is accomplished.
Thou shalt conceive in thy womb, that he might shew that our Lord from the very Virgin’s womb, and of our substance, took our flesh upon Him. For the Divine Word came to purify man’s nature and birth, and the first elements of our generation. And so without sin and human seed, passing through every stage as we do, He is conceived in the flesh, and carried in the womb for the space of nine months.
Gregory of Nyssa: While the expectation of child-birth strikes a woman with terror, the sweet mention of her offspring calms her, as it is added, And thou shalt call his name Jesus. The coming of the Savior is the banishing of all fear.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. III (London: Rivington, 1843).