I found myself mentioning to a friend the other day that my personal journey from raised Catholic to saved Evangelical, among the many big changes, bore a change at how I look at Holy Week. As a Catholic, it seemed the emphasis was always on the Crucifixion rather than the Resurrection (which I would suppose explain why Mel Gibson never did an Easter movie). Of course, everything that Good Friday symbolizes- our guilt, Jesus' payment for our transgressions- that IS important as a first step. But in the Protestant/Evangelical world, the emphasis is on the empty tomb, without which the sacrifice would have been meaningless.
In the Bible, in the OT you can find many examples of Jesus' suffering prophesied. Isaiah 53; Psalms 22; Daniel 9, just to mention a few. To find allusions to the Resurrection are a little trickier, and the message is not near so clear as that of the Messiah suffering. But if Messiah is to have the ultimate victory, as promised by God in Genesis 3:13, SOMETHING has to happen. David tells us in Psalm 16 that God will not allow His Holy One to see corruption; Isaiah in 53:10-12 talks of how He shall prolong His days.
In the New Testament, Jesus points out that the story of Job being saved by the great fish was a presaging of the Resurrection, and so was the Bronze serpent of Moses. But one from those days would hardly see these events as applying to the Savior; Zechariah 9 even gives the story of Palm Sunday- and then suddenly leaps ahead to Messiah's return. So why is the OT so quiet on the subject?
An atheist might say, "Because Jesus and his cronies made it all up." But guess what? Paul mentioned over 500 witnesses, daring people to prove him wrong- and it never happened. If it were all an elaborate con game, what would be the purpose? And in I Corinthians 15, Paul makes it clear- if the was no Resurrection, he and the Apostles weren't mistaken they were LIARS. The Resurrection happened. So back to the original question.
Because the OT is God's Word to the Jews; and while a Jew CAN be saved as the Gentiles have been by the Cross, THEIR day is coming when the Church is removed, the "lawless shepherd comes, and Christ returns for them to "look upon Him whom they pierced as one would mourn an only child". Their final salvation shall be a different thing than ours. Gentiles are required to know Christ by faith; Jewry will have a chance to see Him return and say, "OMG, it WAS Him!" or something a little more respectful along those lines.
But one way or the other, if Jesus does not rise, He's just another dead guy. Praise be to the Lord Christ, for laying His life down for us- and picking it back up again!