v. 14 Therefore the Lord himself will give you a sign. Look, the young woman is with child and shall bear a son, and shall name him Immanuel.
Ah, we say, we know that one! And so did Matthew, writing his Gospel, he has the angel Gabriel quote to Joseph, "Look, the virgin shall conceive and bear a Son, and they shall name him Emmanuel," and he goes on to explain, "which means, 'God is with us." (Matthew 1:23).
In Matthew's quote we notice a few differences. Last one first, the different spelling of "Emmanuel." "E" would be from Greek, "I" from Hebrew. A clue! Matthew is using a Greek text of the Hebrew Scriptures (a text we call "the Septuagint," something akin to "the King James Version" in his day). And so this explains the other, big difference: "young woman" (Hebrew) becomes "virgin" (Greek). Reading Isaiah in the Greek version Matthew had in front of him led him to his own "Aha!" moment. Here is a prophecy of the virgin birth of Jesus.
And Christians have ever believed it so. And so it might, indeed, be. But Christians must also take care to let the Hebrew Scriptures tell their own story (not necessarily the one we want them to tell). Ripping a verse out of its context does violence to the text. Unfortunately, "proof texting" (this act of ripping a text out of its context) is something that is in the Christian DNA, at least since Matthew. It usually gets us into trouble.
Having said all that (which must be said--at least by me!), we have this wonderful word in both texts: Emmanuel, which means God is with us, or God is for us. For both Hebrew and Christian traditions it is an ecapsulation of the gospel, the good news. God is for us, not against us.
It is what Isaiah was trying to get across to the rather thick-headed King Ahaz in his day. It is what Gabriel was trying to get across to the tradition-bound Joseph in his day, and it is what God is still trying to get across to us fearful doubters in our own day. The news is good. God is with us.