I believe some prophets of God, such as Moses and Elijah, are in heaven, yet they lived and died before Christ came. How is this possible? What does this mean for the other Jewish people?
The basic answer is that there is no difference. Old Testament people, Jew or Gentile, who believed in a coming Messiah were saved. Old Testament people who did not have faith were not saved. There is no difference. They are saved 'looking forward' to Messiah. We are saved 'looking back' to Messiah. His actual coming into time to complete his work was not required to be saved by faith in it because since God exists out of time, all that he planned was from eternity and effectual for salvation before he came. God saw Christ as being crucified before the creation of the world in the sense that whatever He planned in time is as creation as history.
But some might say, how did Abraham know about the Messiah. Well originally Messiah ws promised to Adam and Eve. God spoke to the serpent in front of them saying:
Later this promised seed from the woman, was promised to be the seed of Abraham, and Abraham had great faith in Messiah as he and his wife was beyond child bearing years. God said that this Messiah would cause all nations to obtain blessing from God, not just to his biological children:
We know for sure that Abraham has faith in Messiah. Even Jesus declared it:
So you see both Jew and Gentile, before and after Christ, can be saved by simple faith in Jesus for the forgiveness of our sins. Any humble person who acknowledge their need of forgiveness and hopes in Messiah will be saved and is a child of Abraham having the same faith as he had.