Simon's death is pretty brutal. It is meant to represent Christ's crucifixion by his own people as Simon is clearly Golding's Christ figure. The irony of course is that Simon stumbles out of the jungle to spread the "good news". Their beast is not the threat the boys interpreted it as. The boys mistaken their saviour as the beast and violently stab him to death. As Simon enters the scene the boys have already worked themselves into a mindless rage, “Kill the beast! Cut his throat! Spill his blood!” When Simon appears, the boys turn on him,
"The sticks fell and the mouth of the new circle crunched and screamed.
The beast was on its knees in the center, its arms folded over its face. It
was crying out against the abominable noise something about a body on
the hill. The beast struggled forward, broke the ring and fell over the
steep edge of the rock to the sand by the water. At once the crowd surged
after it, poured down the rock, leapt on to the beast, screamed, struck,
bit, tore. There were no words, and no movements but the tearing of
teeth and claws."
Golding has Simon literally become the beast (as seen by the boys) further highlighting the tragic irony of the situation.