Jack and the other boys in his camp, are becoming more in danger of madness. We see how Jack is keeping them worked up about the beast on the island. When all the boys see Simon, they jump on him and kill him. Ralph and Piggy are the only ones who feel bad about what they have done. Jack tries to keep control over the boys, by telling them that was the beast and they had no choice but to kill him. He tells them that the beast is still out there and will disguise itself as anyone, so they must always be on guard against it.
When they take Simon's body out to sea, we are seeing that Simon was the innocent one on the island. He lived in reality and wasn't swayed by Jack's antics.
"Surrounded by a fringe of inquisitive bright creatures, itself was a silver shape beneath the steadfast constellations, Simon's dead body moved out toward the open sea."
This quotes shows us how special Simon was. He was an innocent victim of the boy's madness burning within them.