Behold, thou shalt conceive in thy womb The angel adapts his words, first to Isaiah's prophecy, (Isaiah 7:14,) and next to other passages of the Prophets, with the view of affecting more powerfully the mind of the virgin: for such prophecies were well known and highly esteemed among the godly. At the same time, it ought to be observed that the angel did not merely speak in private to the ear of the virgin, but brought glad tidings, (euangelion,) which were shortly afterwards to be published throughout the whole world. It was not without the purpose of God, that the agreement, between ancient prophecies and the present message respecting the manifestation of Christ, was so clearly pointed out. The word conceive is enough to set aside the dream of Marcion and Manichaeus: for it is easy to gather from it that Mary brought forth not an ethereal body or phantom, but the fruit which she had previously conceived in her womb. Thou shalt call his name Jesus The reason of the name is given by Matthew: for he shall save his people from their sins, (Matthew 1:21.) And so the name contains a promise of salvation, and points out the object for which Christ was sent by the Father into the world, as he tells us that he "came not to judge the world, but to save the world," (John 12:47.) Let us remember that not by the will of men, but by the command of God, was this name given to him by the angel, that our faith may have its foundation, not in earth, but in heaven. It is derived from the Hebrew word ys, salvation, from which comes hvsy, which signifies to save. It is a waste of ingenuity to contend that it differs from the Hebrew name yhvsv, (Jehoshua or Joshua.) The Rabbins everywhere write the word Jesu; and they do this with evident malice, that they may not bestow on Christ an honorable name, but, on the contrary, may insinuate that he is some pretended Jew. Their manner of writing it, accordingly, is of no more importance than the barking of a dog. The objection that it is far beneath the dignity of the Son of God to have a name in common with others, might equally apply to the name Christ, or Anointed But the solution of both is easy. What was exhibited in shadow under the law is fully and actually manifested in the Son of God; or, what was then a figure is in him a substance. There is another objection of as little weight. They assert that the name of Jesus is not worthy of veneration and awe, that at the name of Jesus every knee should bow, (Philippians 2:9, 10,) if it does not belong exclusively to the Son of God. For Paul does not attribute to him a magical name, as if in its very syllables majesty resided, but his language simply means that Christ has received from the Father the highest authority, to which the whole world ought to submit. Let us then bid adieu to such imaginations, and know, that the name Jesus was given to Christ, in order that believers may be instructed to seek in him what had formerly been shadowed out under the Law.

And, behold, thou shalt conceive in thy womb - See the notes at Isaiah 7:14.
And shalt call his name Jesus - A Saviour. See the notes at Matthew 1:21. All this was announced. also, by an angel to Joseph, after this visitation to Mary. See the notes at Matthew 1:20-21.

Thou - shalt call his name Jesus - See on Matthew 1:20, Matthew 1:21 (note), and here, on Luke 2:21 (note), and John 1:29 (note).

And behold thou shalt conceive in thy womb,.... Though a pure virgin, which never knew a man; and therefore, "a behold", is prefixed to it, as being what was extraordinary and wonderful; as it is also, in the prophesy of it, in Isaiah 7:14 to which the angel manifestly refers, and is, by Matthew cited, as accomplished hereby; see Gill on Matthew 1:22, Matthew 1:23.
and bring forth a Son, and shalt call his name Jesus; which signifies a "Saviour"; and a Saviour Christ is of God's appointing, providing and sending; and a very suitable one, being a spiritual Saviour, and a complete one, both able and willing to save to the uttermost all that believe in him; nor is there any other, nor salvation in any other: he is the Saviour of his people, whom the Father has given him, even of all the elect, whether of Jews or Gentiles; and of them from all their sins, and from all their enemies; and whom he saves with a spiritual and eternal salvation.

The angel purposely conforms his language to Isaiah's famous prophecy (Isaiah 7:14) [CALVIN].