The gospel of Matthew has 28 chapters; the last 8 of them are spent on the week stretching from Palm Sunday to the Resurrection. The other gospels have a similar emphasis: not only the largest section, but the pride of place as culmination and climax is given to Jesus' death and resurrection.
I remember, years ago watching Mel Gibson's Passion of the Christ, the scene -- was it a flashback? -- where a woman caught in sin was forgiven by Jesus. The look in her eyes when Jesus was led off to execution seemed to ask a question: if Christ is executed, is forgiveness still the last word for me? Or am I next?
Death takes all of Jesus' miracles and gives them over to the powers of darkness, where we hear a mocking, "So what?" to them all. If Jesus stays in the tomb, eventually the miraculous bread is gone, the storms are back, sickness is back, forgiveness is gone, death is back, and that is the last word. If Christ is not raised, that forgiveness he announced to us is not the last word. If Christ is not raised, the powers of darkness win and the kingdom of God is not among us.
I have heard some Christians say that some groups over-emphasize the cross of Christ: that it is not so central to Christianity, that Jesus should not be portrayed on it, that Christian thought and devotion and artwork overemphasizes what happened there. But Matthew, Mark, Luke, John, Peter, and Paul all put the focus on Jesus' death and resurrection. We can shy away from it because it is difficult to wrap our minds around. We don't necessarily appear at our most sophisticated when we struggle to grasp and articulate everything that has happened there. Paul said it very succinctly, that given the choice of talking about miraculous signs, or wisdom, or Christ crucified, he knew what he would choose: "While I was with you, I resolved to know nothing but Christ, and him crucified."