Simon's encounter with the Lord of the Flies reinforces Golding's most central theme of the novel, that man is innately evil. As the boy on the island with clearly the most insight, Simon realizes the potential explanation for the beast early on in chapter five, when he says "maybe it's only us" (89). Simon's encounter with the Lord of the Flies in the jungle confirms his worst suspicions. In a moment both fiercely horrifying and symbolic, Simon's meeting with the Lord of the Flies captures the isolation and desperation of the boys, coupled with the growing magnitude of the boys' savagery.
The Lord of the Flies is a religious allusion to Beelzebub, which translated literally means "Lord of the Flies" (Notes on Lord of the Flies 205). The symbol derives from the sacrificial offering left by Jack for the beast, a sow's head covered in flies.
"They were black and iridescent green and without number; and in front of Simon, the Lord of the Flies hung on his stick and grinned" (138).
In Simon's hallucinatory state, he struggles to separate dreams from reality. The Lord of the Flies represents the epitome of evil, and taunts Simon that the beast is from within:
"You knew, didn't you? I'm part of you? Close, close, close! I'm the reason it's no go? Why things are what they are?" (143)
The Lord of the Flies reveals this knowledge to Simon deep in the heart of the jungle, surrounded by nature and the swarms of flies as Golding's own representation of the truth: Evil will inherently tempt man in his natural state, away from the structures and confines of civilization.