It's interesting how Jesus was never called Immanuel. It's also interesting how that "prophecy" from Isaiah 7 had nothing to do with Jesus in the first place. At that time, the Judahite were under attack from two kings - Rezin, king of Aram and Pekah, king of Israel. The people of Judah, under King Ahaz, were in fear. G-d begins by telling Isaiah to speak with Ahaz to let him know these two kings will no prosper in their bid to take over the people of Judah. He (G-d) then told Ahaz to ask for a sign from Him that His words were true. Ahaz declined and said he would not put G-d to a test. G-d gave him a sign anyway:
"'Therefore, my Lord Himself will give you a sign: BEhold, the maiden will become pregnant and bear a son, and she will name him Immanuel. ... For before the child will know to abhor evil and choose good, the land of the two kings whom you fear will be abandoned.'" Isaiah 7:14, 16
First of all, the Chrsitian Bible utilizes the Greek Septuagint (sp?) translation of the Tanakh - an innacurate translation. The word translated as "virgin" in the Christian OT is a mistranslation and should simply read "maiden" or "young women" - not necessarily a woman who has never had sexual relations. The Hebrew word used is "ha'almah". If the author wanted to portray the idea that this young woman was a virgin, the word "betulah" would have been used instead. The word used for conceive, as well, is actually written in the past tense, meaning the child had already been conceived, though the pregnancy was in such early stages that it was "hidden" from the people. As well, the child, called Immanuel, would have to learn the difference between evil and good, something illogical with the idea that Jesus was G-d incarnate. And, by the time the child was old enough to differentiate between good and evill, the land of the two kings (the king of Aram and the king of Israel/Ephraim) would be abandoned. And it was.
Passover is about deliverance from death. The Passover lamb was slain in PLACE of the first born son. That is the whole point. Jesus was the lamb that was slain in our place to deliver us from spiritual death.
Christianity has to do some major logical summersaults to get from a physical, one-time event of the passing over of the first-born Israelite child to the spiritual salvation of the entire world. It just plain ol' doesn't add up with what the Passover offering was, and why it happened. It was only one time that the Israelites painted the blood upon the lintels. Every Passover thereafter is to serve as a remembrance. No sin offering, no "spiritual" salvation ... just a rememberance of what happened in the Egyptian desert when G-d killed the first born of each Egyptian household.