The idea of 'Good versus evil' is one of the dominant themes of Lord of the Flies. William Golding once described this theme of the novel as "an attempt to trace the defects of society back to the defects of human nature" (qtd. in "Notes on Lord of the Flies" 204). As the boys learn to fend for themselves on the uninhabited island, the novel explores civilization's struggle against man's basic instinct for savagery and evil.
One of the defining moments in the novel occurs when Simon encounters the Lord of the Flies, the embodiment of decay, destruction, and evil. The Lord of the Flies, an "obscene thing on a stick," mocks the boys' fears: "Fancy thinking the Beast was something you could hunt and kill;" Simon's conversation with the evil entity reveals an important truth of the novel--the Beast, the great evil of the island, is not some monstrous creature, but is actually the boys themselves (142).
Golding utilizes the scene with the Lord of the Flies and Simon to reinforce his theme of good versus evil; ultimately, the author wants to convince the reader that the integrity of civilization depends upon the individual's struggle against his own baser nature. Ralph and Jack are perfect character examples of Golding's theme. Ralph fights against his savage impulses and tries to maintain order on the island; he remains a moral character that held onto his responsibilities and looked out for the well-being of others. On the other hand, Jack epitomizes the message of the Lord of the Flies in the way that the boy embraces savagery and violence as a means of control and power.
*"Notes on Lord of the Flies" by E. L. Epstein, found in this edition of the novel: Golding, William. Lord of the Flies. New York: Perigree Books, 2006.