For another thing, it is certain that the word almah is never used to refer to a married woman. This is true even in those occasions when the context does not allow us to say with certainty that almah must refer to a virgin. Martin Luther was so confident about this point that he actually offered 100 Gulden—which, from what I can tell, would be something like $45,000 today—to anyone who could prove that almah was used in reference to a married woman anywhere in the Old Testament. And neither Luther, nor anyone else since then, has ever had to pay up. That is because the word always refers to an unmarried woman who is of marriageable age.
Old Testament Judaism was not a culture that was known for its promiscuity, at least not among its young women. Jewish law required the death penalty to be administered to any unmarried young woman of marriageable age who was found not to be a virgin (Deut. 22:13–21). That means that in Isaiah’s day, the expectation among all the people would have been that an unmarried young woman of marriageable age would necessarily be a virgin.
Second, the context of Isaiah 7:14 indicates that the best translation for almah must be “virgin” and not simply “young woman of marriageable age.” God is providing a sign for unbelieving King Ahaz. And it is hard to see how a “young woman of marriageable age” who conceives and bears a son would qualify as a sign from God. By definition, a sign must be something extraordinary. Otherwise, how does one know that it actually is a sign? A young woman bearing a child out of wedlock certainly would be notorious, but it would hardly be extraordinary in a way that would be worthy of God. He is not only perfectly righteous and holy, but He requires His own people to be holy precisely because He is Himself holy (Lev. 19:2). The whole point of Isaiah 7 seems to be that God’s sign would be an extraordinary (not notorious) child who would be brought into the world by way of an extraordinary (not notorious) birth. He would be human and divine—human, because He would be born of a woman, and divine, because He would be “God with us.” He could not, therefore, come into the world in the same way that every other child does. His birth had to have been special. His birth had to be a virgin birth. If it wasn’t, then the resulting child could only be human. He could not be Immanuel, God with us.
Third, the Greek translation of the Hebrew Old Testament, the Septuagint, confirms that almah is best interpreted as “virgin” in Isaiah 7:14. It translates this verse by using the Greek word parthenos, which more explicitly denotes a virgin, rather than neanis, which more generally means a young woman. Moreover, the gospel accounts in Matthew 1 and Luke 1 both use the Greek word parthenos of Mary and do so in a context that explicitly portrays her as a virgin. In Matthew 1:18, for instance, we read that Mary becomes pregnant “before [she and Joseph] came together.” That is why Joseph resolved to break off their engagement. He knew that he was not the father of the child she was carrying (v. 19). No doubt he would have gone through with his plans to put Mary away were it not for the “angel of the Lord” appearing to him in a dream and telling him that the child within Mary’s womb was not from a man but “from the Holy Spirit” (v. 20). Matthew then goes on to quote Isaiah 7:14 and to say, under the inspiration of the Holy Spirit, that its prophecy is fulfilled in the virgin birth of Jesus. That is just what we would expect, given everything we have seen about Isaiah 7:14.
Similarly, in Luke 1:27, Mary is twice called a “virgin” (parthenos) and is told by the angel Gabriel that, while still in that state, she will give birth to a son who “will be great and will be called the Son of the Most High” (vv. 31–32). Understandably, Mary questions Gabriel and asks how this will be since, as she herself says, she has never been with a man (v. 34). Gabriel answers by telling her that no man will be involved in the process. It will be an extraordinary birth: “The Holy Spirit will come upon you, and the power of the Most High will overshadow you.” And the Spirit’s power will produce an extraordinary child: “the child to be born will be called holy—the Son of God” (v. 35).
For all of these reasons, we can be confident that a virgin really did give birth. Not only is this the kind of thing that is to be expected given the fact that a supernatural God exists, but this is the very thing that we should expect in itself, given the fact that the Bible tells us so. Isaiah 7:14 predicts that a “virgin”—and not just a “young woman”—would give birth to a son who would be both divine and human, and the Gospels record the fulfillment of that prediction in the life of Mary and Jesus. The glory of Christmas is that the expectation of Isaiah 7:14 has become a reality. The virgin really did give birth to a son. He was called Immanuel, for He really was God with us. And He was given the name Jesus, because He really did save His people from their sins (Matt. 1:21). That is why we sing, “Joy to the world! The Lord has come.”