What significance does Simon's opinion of the "beast" have on the boys?
In Chapter 5, Ralph holds an assembly meeting and tries to come to a conclusion regarding the existence of the beast. Several boys have different views on the beast, but only Simon understands the true nature of it. Jack dismisses its existence and suggests the boys "get over" their fears. Piggy doesn't believe in the beast either but attempts to solve their fears pragmatically. Simon has a hard time articulating his thoughts and can only compare "mankind's essential illness" to the dirtiest thing the boys can think of. The boys begin laughing at Jack's expletive response and dismiss Simon as crazy.
Golding uses Simon's character to illustrate the true nature of the beast and comment on the dark, primitive instinct of humanity. A major theme throughout the novel is the true nature of mankind void of societal boundaries and restrictions. Golding suggests that humans have an innate, savage instinct that opposes civility and morality. Simon is an allegorical Christ figure throughout the novel. His insight allows the reader to grasp Golding's concept of humanity, while portraying his character as enlightened. In the aftermath of Simon's death, the boys quickly descend into complete barbarism.
The boys are unable to comprehend Simon's thoughts on the beast and dismiss him as crazy. Their lack of understanding illuminates how "lost" they are and symbolizes the Jewish population's rejection of Jesus.
The moment that Simon comments on "man's essential instinct" is significant because its display his recognition of mankind's propensity for evil and the boys' inability to recognize their flawed nature. It also emphasizes the significance of his death later on in the novel that highlights the moral degradation of the boys.