It is well to admit that interpreting the details of Isaiah 7:14 in its context cause difficulty and consternation. Most all conservatives can agree on the remote fulfillment in Jesus born of Mary, a virgin, while wrangling over the immediate application (if there is one).
The two main ideas I have seen regarding this as a dual prophecy are that the immediate Immanuel is:
- Hezekiah, the son of Ahaz, or
- Maher-shalal-hash-baz, son of Isaiah
These to have the following difficulties. The mathematics of Hezekiah's age when he became king shows he was already born before this time (He was 25 years old when he began to reign, and Ahaz's reign only lasted 16 years). God told Isaiah to name his second son Maher-shalal-hash-baz, which is not the same name and means something different than Immanuel. The rank assigned to Immanuel in Isaiah 8:8 also doesn't seem to fit Isaiah's son.
Another interpretation (which I hold, but have not heard as often, and which is not without some difficulties of its own) is that (1) verses 14-15 concern Jesus, the Immanuel, God with us, and is a sign to the house of David (
you, plural, v. 14), and that (2) and verse 16 concerns Isaiah's son Shearjashub, who Isaiah brought with him, and is a sign to Ahaz (
thee, singular, v. 7). This includes an immediate sign that Ahaz can "read" (i.e., before Isaiah's son knows enough to refuse the evil and choose the good, two kings will be destroyed, verses 8-9, 16), and a future sign to the nation of the coming Messiah.