Isaiah 7:14

A virgin] The Hebrew word is not the distinctive one for virginity, but denotes rather one of maturing and marriageable age: cp. e.g. Genesis 24:43; Exodus 2:8. In the first place, this prophecy must have been intended by Isaiah as a sign of encouragement to Ahaz—before a child, shortly to be born, could arrive at years of observation the enemies of Judah would be brought to nought. At the same time, it is evident that the child is no ordinary one, from the way in which the prophet refers to him as Lord of the land (Isaiah 8:8), and from the titles given to him in Isaiah 9:6. The child is, in fact, the Messiah, whose advent Isaiah seems to have expected in the near future in connexion with the Assyrian invasion (Isaiah 9:1; Isaiah 11:1). The prophet's anticipations were realised, but in a manner far surpassing his expectations, in the birth of our Lord.

Immanuel] i.e. 'God is with us' (Isaiah 8:10). The child whom the prophet has in mind received this symbolic name as being a pledge of God's presence with His people. Christ, the true Son of David, is in the highest conceivable sense Immanuel. The sign given by Isaiah is not concerned with the manner of the child's birth, but rather connected with his name Immanuel. Accordingly in Matthew 1:23 the emphasis is upon the name.