What is the significance of the resurrection, you ask?
Well, as an evangelical Christian, here is my answer:
Well, the short form of the gospel is this:
No one is perfect. No one is holy. Our falling short of this is called "sin."
God demands holiness. Therefore, our sin separates us from Him. In the current world, sin permeates the world, so there is sickness and death and rebellion.
God, in His physical presence aspect (God the Son) dealt with sin by becoming a man - Jesus of Nazareth (the Messiah, or Christ). As a man, he lived a perfect life. He eventually was crucified, and in dying on the cross, he paid the penalty for mankind's [by which I mean all humans'] sins. Being infinite God, he was able to pay the sin penalty in a finite amount of time (as opposed to being separated from God for all eternity, which is the penalty for any other human), and being human he was able to pay the penalty for humans at all.
As sin is the root cause of death, and as Jesus took all sin upon Himself, he would have to remain dead as long as any of that sin remained unpaid for. Therefore, raising Himself from the dead proved that he had taken care of sin once and for all.
(Of course, there is a catch. For his payment to be effective for a person, it has to be accepted. Which is why one must believe in Jesus to be saved).
That is all for this post.