what does the final images of Simon reveal about his role on the island?

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 spiritual) Golding leaves us no doubt that Simon was the boys' Christ figure and he is sacrificed.Note the soft and spiritual imagery of Simon's dead body,

"Surrounded by a fringe of inquisitive bright creatures, itself a silver shape beneath the steadfast constellations, Simon's dead body moved out toward the open sea."