Sorry, this will be a bit long,
We must first understand what Simon represents in the novel. From the beginning, Golding develops Simon as a Christ-figure. Simon takes on many of the characteristics that Christ had. Simon does not say too much but when he does speak it is to reveal some sort of truth. He defends the weak (Piggy,littluns) and he prefers to think in solitude. Simon is the only boy who understands the nature of the Beast; he knows the beast lives within all the boys. So, it is fitting when Simon scrambles down the mountain to tell the boys the "good news" (The beast that they see is just a dead pilot), Simon is brutally killed. In trying to save the boys from themselves Simon is murdered. If you check out the last paragraph when Simon is killed (the language turns almost spiritual) Golding leaves us no doubt that Simon was the boys' Christ figure and he is sacrificed.
The Island is also turned from Biblical like Eden to a literal and figurative Hell. Hell becomes a place where the "weak" and sympathetic are punished and the "strong" and ruthless are rewarded. One of my favourite lines comes earlier on in the book when Piggy is watching the boys dance around the giant fire, "Piggy glanced nervously into hell and cradled the conch." For a guy like Piggy and, to a lesser extent Ralph, this is literally and symbolically Hell. It is a place where disorder and destruction rule. The Pig's head on the stick "The Lord of the Flies" is a derived from the latin Beelzebub or devil. It attracts and corrupts. It asserts itself as the driver behind the boys' hearts and minds.