The prophecy of Isaiah 7:14 is a very controversial passage, primarily for two reasons. First, the meaning of the Hebrew term almah in 7:14. It is translated “virgin” in the ESV, but could also be translated “a young unmarried woman.” Second, the time frame for fulfillment of the birth of Immanuel. Several verses (7:16; 8:8b, 10) seem to suggest that Immanuel would be born in the immediate future. When we come to the NT, however, Matthew teaches that this was a prophecy of the virgin birth of Jesus (1:22-23), using the specific Greek term for virgin, parthenos.
So was Isaiah speaking about a child in his day, Jesus, or both? I think a key to understanding this and many other prophecies is the concept of typology. A type is a category. And within that category there can be greater or lesser examples. For instance, “son” is a category. Israel was an example of a son, in the sense that the nation had a father-son relationship with God (Ex. 4:22-23). However, Israel was in most respects a very poor son (Hosea 11:1). Jesus was also a son, but he was the ultimate example of what a son should be. This is why Matthew can say Jesus “fulfilled” Hosea 11:1 – not because he was the only son God had, but because he was the ultimate model of what a son should be. So both Israel and Jesus could be categorized as “sons,” but within that same type or category of sonship they were vastly different examples of sons.
It seems to me that essentially the same thing is going on in Isaiah 7:14. The prophecy is of a son whose name indicated the presence of God. And Isaiah’s own sons indeed indicated God’s presence, either in judgment (Maher-shalal-hashbaz) or redemption (Shear-jashub). But these were only secondary models of the ultimate son whose birth would indicate God’s presence. And while Isaiah’s sons were important examples of signs from God, neither of them could begin to match the description of the ultimate son described in Isaiah 9:1-7. And that is what Matthew is teaching in his gospel. He is showing that Jesus is the ultimate “Immanuel.”
There are hints in Isaiah that “Immanuel” must have a meaning beyond his own children. First, “Immanuel” does not have the same kind of direct relevance to the historical situation as do the names of his other sons. Further, the sign of Immanuel was given not just to one king, but to the “house of David” (7:13). In fact, the Hebrews pronouns “you” and “your” are plural in verses 9, 13, and 14. Finally, the close proximity of the Immanuel passage to 9:1-7 suggests a much bigger picture than a mere son of Isaiah (as Matthew confirms in Matt. 4:14-16).