Earlier today in chat, I saw this:
Jewish identity is matrilinial. Jewish tribal lineage is patrilinial.
If Jesus had no biological father, then he could not be from the tribe of Judah, as the Messiah will be. From a Jewish perspective, the irony is that being born of a virgin would not prove that one was the Messiah. On the contrary it would invalidate one as a messianic candidate.
Source: anursa, comments on Slacktivist, via TRiG.
It was asked by fredsbend:
Is that an accurate depiction of Jewish thought? That is interesting.
and affirmed by HodofHod:
Now, as a Christian, I seem to recall some prophecy about the Messiah necessarily being born of a virgin. Sure enough, I see that Isaiah 7:14 says
14 Therefore the Lord himself will give you a sign: The virgin will conceive and give birth to a son, and will call him Immanuel. - Isaiah 7:14 (NIV)
But wait, that's a Christian translation. Enter the JPS...
14 Therefore the Lord Himself shall give you a sign: behold, the young woman shall conceive, and bear a son, and shall call his name Immanuel. - Isaiah 7:14 (JPS)
...and Judaica Press translations.
14 Therefore, the Lord, of His own, shall give you a sign; behold, the young woman is with child, and she shall bear a son, and she shall call his name Immanuel. - Isaiah 7:14 (Judaica Press)
(All emphasis mine.)
Okay, so the term can also be translated "young woman". So, now the question is: why is it so significant that a young woman conceive and bear a son? I'd figure that young women would be conceiving and giving birth all the time back in the old days.
Note: HodofHod also pointed out in chat that the "young woman" part isn't the significant thing, but the unaware naming of her child Immanuel. This would be an acceptable answer, as it does answer the question in the title about how the verse should be interpreted.