Looking back at the Old Testament through the lens of the New, it is easy to assume that Isaiah understood the Messianic meaning of his prophecy. However, those who believe that the Bible is the infallible repository of redemptive revelation must be willing to test all things in light of Scripture and hold fast to that which is good (1 Thessalonians 5:21).
First, the prophecy in Isaiah chapter seven—“the virgin will be with child and will give birth to a son, and will call him Immanuel”—was fulfilled in Isaiah chapter eight. As Isaiah makes clear, this prophecy was fulfilled when Isaiah “went to the prophetess, and she conceived and gave birth to a son” named Maher–Shalal–Hash–Baz (8:3). In context, Judah “was shaken” as two powerful kingdoms sought the nation’s demise (7:1–2). God, however, promised that the birth of Maher–Shalal–Hash–Baz was a sign that Judah would be spared. In the words of Isaiah, “Before the boy knows enough to reject the wrong and choose the right, the land of the two kings you dread will be laid waste” (7:16; cf. 8:4).
Furthermore, though Isaiah’s wife, unlike Mary, was not a virgin when she gave birth, she nonetheless was the near–future fulfillment of Isaiah’s prophecy. “Virgin” (almah) was simply a term used to refer to the prophetess prior to her union with Isaiah, not to indicate that she would give birth to a child as a virgin. By way of analogy, it would have been true in 1999 to say that “the governor of Texas will one day lead this country,” but this obviously does not mean that George W. Bush would lead the United States as the governor of Texas.
Finally, while the Holy Spirit may have revealed to Isaiah that his prophecy pointed forward to Jesus (John 12:41), it was not until after the miraculous virginal conception and birth of Jesus more than six hundred years later that it became entirely clear that the near–future fulfillment of Isaiah’s prophecy was a type, the archetype of which is Jesus the Messiah (Matthew 1:22–23). While Maher–Shalal–Hash–Baz signified temporal salvation for Judah, Jesus Christ––the literal “Immanuel”––embodied eternal salvation for true Israel.
For further study, see Craig L. Blomberg, Jesus and the Gospels (Nashville: Broadman and Holman Publishers, 1997): 199–200.
“All this took place to fulfill what the Lord had said through the prophet: ‘The virgin will be with child and will give birth to a son, and they will call him Immanuel—which means, God with us.’”