Isaiah - Chapter 7
What Virgin Birth?
Isaiah prophesied in the time of King Achaz of Judah. At the time, R'tzin, king of Aram and Pekach, king of Israel were teamed up against Judah. Achaz was worried, because each of these kings had defeated him alone and now they were combining their efforts.
G-d sent Isaiah and his son, Shor Yoshuv, to Achaz, to tell him to be calm because the aggressor nations would not succeed. Furthermore, in 65 years, the northern Kingdom of Israel would cease to be a nation altogether, because they'll be exiled by Assyria. Then, Achaz was told to choose a sign to prove the prophecy.
"I won't test G-d," Achaz replied. "Oh, please," said Isaiah, "you tire both man and G-d. Fine. I'll give you a sign. The young woman is pregnant and will have a son, whom she'll call Immanuel. Before he's old enough to know good from bad, the land of the two kings that you fear will be abandoned."
The prophecy to Achaz continues: Your kingdom will have a Golden Age like it hasn't seen since the nation split in two. G-d will signal the armies of Egypt and Assyria; He will remove the king, people and governors of Assyria like hair before a razor. A person will only have a few animals, but they will produce so much milk that everyone will live on the cream. Vineyards that had a thousand vines will be desolate. (Radak says that vineyards that were desolate will contain a thousand vines.) Mountains will not be tilled because of worms and thorns, but will be pastures for cattle and sheep.
There are famous non-Jewish sources that interpret verse 14 to refer to a future "virgin birth." Nothing in the chapter supports such a reading. (1) The word alma means a girl, but not necessarily a virgin. (Besulah is virgin.) (2) It also says that the girl "has conceived," not "will conceive." (3) The verse doesn't say "a girl" will have a baby, but "the girl," that is, one known to Isaiah and Achaz. Generally this is taken to be refer to one of their own wives and refer to either the birth of Achaz's son, King Chizkiyahu, or Isaiah's own son, in the next chapter. (4) Perhaps most tellingly, the prophecy is that these attacking nations would be defeated while the child is still quite young. If it foretold the birth of a baby in Bethlehem over 600 years later, it would not be much of a sign to Achaz that he would win, as both the war and his life would be ancient history by then! From context, it had to be a baby Achaz would live to see!