Mary is twice mentioned as a “virgin” (παρθένος) in Luke 1:27. “In the sixth month the angel Gabriel was sent from God to a city of Galilee named Nazareth, to a virgin betrothed to a man whose name was Joseph, of the house of David. And the virgin’s name was Mary” (Lk. 1:26-27). Is this intended to evoke Isaiah 7:14, “Therefore the Lord himself will give you a sign. Behold, the virgin [LXX παρθένος] shall conceive and bear a son, and shall call his name Immanuel”? Some would answer in the affirmative, while others are less inclined to do so. But the parallel between Isaiah 7:14 and Luke 1:31 strongly suggests that Luke does in fact have this verse in mind:
- Behold, you will conceive in your womb and bear a son, and you shall call his name Jesus (Lk. 1:31)
- Behold, the virgin shall conceive and bear a son, and shall call his name Immanuel (Isa. 7:14).
- καὶ ἰδοὺ συλλήμψῃ ἐν γαστρὶ καὶ τέξῃ υἱόν, καὶ καλέσεις τὸ ὄνομα αὐτοῦ Ἰησοῦν (Lk. 1:31).
- ἰδοὺ ἡ παρθένος ἐν γαστρὶ ἕξει καὶ τέξεται υἱόν, καὶ καλέσεις τὸ ὄνομα αὐτοῦ Εμμανουηλ (Isa. 7:14).
In further support of this allusion, Isaiah 7:13 reveals that this sign is addressed to “the house of David,” which is central also to Luke’s narrative: “of the house of David” (Lk. 1:27) and “the throne of his father David” (Lk. 1:32). These clear parallels would have been easily recognized by the original readers, therefore warranting the conclusion that Luke did have Isaiah 7:14 in mind and, more likely, the entire context of Isaiah 7-11. David Pao concurs,
The strong emphasis on the Davidic promise in the immediate context (1:32-33) and throughout Luke 1-2 … makes it likely that the author also recognizes the hermeneutical significance of Isa. 7-9 in explaining the role and identity of Jesus.
Isaiah 7 transitions from the impending judgment of God that will soon befall Judah (Isa. 1-6) to God’s deliverance of a remnant of Israel. The child to be born, according to Isaiah 7:14, will be a sign of this sovereign and gracious deliverance by God. This sheds light on the hymns sung by Mary (Lk. 1:46-55) and Zechariah (Lk. 1:68-79) that comment on the nature of this child to be born, especially pointing to the deliverance and salvation that he brings for Israel:
He has shown strength with his arm; he has scattered the proud in the thoughts of their hearts; he has brought down the mighty from their thrones and exalted those of humble estate (Lk. 1:51).
Blessed be the Lord God of Israel, for he has visited and redeemed his people and has raised up a horn of salvation for us in the house of his servant David, as he spoke by the mouth of his holy prophets from of old, that we should be saved from our enemies and from the hand of all who hate us; to show the mercy promised to our fathers and to remember his holy covenant, the oath that he swore to our father Abraham, to grant us that we, being delivered from the hand of our enemies, might serve him without fear, in holiness and righteousness before him all our days (Lk. 1:68-75).
Furthermore, the idea of a remnant of Israel being delivered also fits with Luke’s emphasis on the peculiar nature of Jesus’ salvation (or “exodus,” Lk. 9:31) and the majority of Israel eventually rejecting him. We can say, then, that Isaiah 7:14 looked forward to Jesus’ day when God would again act in the might of his power to redeem and save his people from their enemies and establish them as a kingdom of priests to serve in his presence where there is fullness of joy. This brings us not only to the heart of Jesus’ birth, but also to the heart of Luke’s entire gospel.
While much more can be said, I want to consider one technical question. Did Isaiah have in mind an actual virgin or just a young girl in his prophecy? And did he have to have a virgin in mind for Luke to legitimately allude to its fulfillment in the virgin birth of Jesus Christ? In most translations of Isaiah 7:14 the Hebrew word עַלְמָה is translated as “virgin” (ESV, NASB, NIV, etc.), though in most contexts it is better rendered “marriageable girl” or “young woman” (NRSV).
If you take it as “virgin” then you have a direct fulfillment of the prophecy in Jesus’ birth to the virgin Mary. But Luke’s tendency is rather to see the history of God’s people in the Old Testament as establishing a program of events that necessarily have to come to pass in Jesus’ life (volume 1: Luke) and then in the apostles’ (volume 2: Acts). In other words, the history of God’s people must be recapitulated in the life of Christ who alone can bring Israel out of her barrenness and into the fulfillment of God’s promises. Green gets at this when he writes,
The conjunction of so many points of correspondence between the Gabriel-Mary encounter and Isa 7:10-17 cannot help but produce an echo effect, though it would be going too far to suggest that Luke wants to narrate the fulfillment of Isa 7:10-17. Rather, these reverberations establish an interpretive link emphasizing how God is again intervening in history to bring his purpose to fruition.
This is an important point that allows a legitimate allusion to be established without requiring the “virgin” (LXX: παρθένος; MT: עַלְמָה) in Isaiah to be a virgin in the same sense Mary was. In fact, it seems that this person spoken of in Isaiah’s time is just a young woman whose pregnancy, which will probably come through natural means, is foretold and is to operate as a sign. This previous sign of the Lord will be imitated or recapitulated on a higher level with the child who is to be born to Mary. God is again—though now in a final, consummative way—graciously providing a son who belongs to the royal house of David to deliver a remnant of his people. But this time will be greater than before, for this Son will be born miraculously to a virgin and in him God will lead a new, even eschatological Exodus.
 Marshall, The Gospel of Luke, 66.
 Fitzmyer, The Gospel According to Luke, 336; Bock, Luke, vol. 1, 61-62.
 The context of the opening of Isaiah can be summarized as such: “(1) God’s coming judgment upon Judah (chaps. 1-6), (2) subsequent deliverance for an Israelite remnant (7-12), and (3) prophecies condemning the nations surrounding Israel (13-23)” (Beale, Handbook on the New Testament Use of the Old Testament: Exegesis and Interpretation, 135).
 Pao, “Luke,” in Commentary on the New Testament Use of the Old Testament, eds. G.K. Beale and D.A. Carson, 259.
 Green, The Gospel of Luke, NICNT, 85. While Green cautions against using the word “fulfillment,” it still may be used if it is understood in the sense of recapitulation, a broader prophetic fulfillment of events and actions than direct prophetic words (see Beale, Handbook on the New Testament Use of the Old Testament, 16n44; 58; idem., A New Testament Biblical Theology, 951-57, esp. 956).
 It is interesting that in Justin Martyr’s dialogue with Trypho the Jew in the second century, Trypho does not understand Isaiah to be speaking about a “virgin,” as Justin does, but a “young woman.” See chapters 66 and 67 of Justin’s Dialogue.