The Old Testament Passage

The inclusion of this particular passage from Isaiah is based entirely on the fact that verse 14 is quoted in the Gospel passage (vs. 23). There are two issues to be commented on here:

1. The designation of the one who is to give birth as a "virgin" or young woman. In the Hebrew language the reference is clearly to a young woman with no connotation as to her chastity. The JPS TANAKH reads "...the young woman is with child and about to give birth to a son." But the Gospel passage is quoted from the LXX not the original Hebrew and uses the same greek word parthenos which means a young woman with out blemish or virgin. I think, that whatever the original Hebrew writer meant, clearly by the time of the translation of the LXX, the meaning was the same as our modern-day understanding of virgin. It is interesting to note that Paul, whose letters pre-date the destruction of the Temple and the final redaction of the Gospel of Matthew, appears not to have known of the tradition of the virgin birth. At least, he makes no mention of it in his letters, from which one can safely conclude, in my opinion, that the doctrine had no relevance for him if he did know of it.
2. The second issue with the Isaiah 7:14 passage is the name of the child who is to be born: Immanuel, which means in the Hebrew "with us is God."(JPS TANAKH)
   

   1) god, god-like one, mighty one 1a) mighty men, men of rank, mighty heroes 1b) angels 1c) god, false god, (demons, imaginations) 1d) God, the one true God, Jehovah 2) mighty things in nature 3) strength, power (Whittaker's Revised BDB)

The Greek word used in the LXX and the Gospel passage is Emmanouel which is a transliteration of the Hebrew into Greek.

God with us. The implication here is that the child born to the young woman is bringing God to the rest of the people. In him is the embodiment of the divine.

From the Mercer Dictionary of the Bible: Immanuel occurs in the prophecy of Isaiah during the Syro-Ephraimitic crisis of ca. 735 B. C. E. The prophet was seeking to give King Ahaz the assurance that God was with him as he faced the terror of invading armies.