How is the theme good vs. evil evident in the novel Lord of the Flies?
In the novel, there are many examples of good versus evil. Golding inserts in the novel many Christian symbols--the hit-you-over-the-head kind. For example, Simon is the Jesus figure: he is kind, works on the huts (Jesus was a carpenter), feeds the children fruit that they cannot reach (Jesus fed people in the Bible), and he goes to a private place with natural candles on the trees to meditate (similar to going to a church to pray). Simon is also the one who has the standoff with the beast--the boars head on the stick. This is where the beast informs Simon that there is no beast to be afraid of: they only have to be afraid of themselves--the beast within.
Furthermore, many experts believe that Jesus had epilepsy (a seizure disorder), and Simon has this condition, too. He has a seizure at the end of his conversation with the beast, which is why he has so much trouble walking down the mountain after he wakes up. He slinks down the mountain, hunched over, and the kids (at first) mistake him for the Beast. But then they know who it is and they kill him anyway--good versus evil again. As his body floats away, the head is surrounded by bioluminescent creatures that make a "halo" around it.
Then there is Jack versus Ralph. Jack creates a tribe, one that sacrifices animal parts to the Beast--very reminiscent of young civilizations. Maybe the Beast will be pleased and won't hurt them if they sacrifice these pigs heads. They have moved from science to superstition. Jack's henchmen, Roger and Maurice, are as evil as they come. Roger tortures kids, and he eventually kills Piggy with a large boulder.
Jack, at the end, reverts to human sacrifice, with a stick "sharpened at both ends" for Ralph, as he plans on sacrificing Ralph's head to the Beast. Then Jack's entire tribe hunts Ralph until they are rescued by the adults. All of the kids, with the exception of Simon, have let their inner beast out on the island at some point.
Certainly, an argument can be made that the narrative of William Golding's Lord of the Flies is Biblical; for it follows the concept of Total Hereditary Depravity:
'All men are born in sin, children of the devil, totally depraved.' One is sinful, therefore, by nature of one's birth, rather than by willful rebellion against God. (Canons of Dordt)
This concept of infant depravity and sin is one embraced by many Christian religions; it is mentioned in the book of Genesis:
And God saw that the wickedness of God was great in the earth and that every imagination of the thoughts of his heart was only evil continually (King James Bible-Genesis 6:5)
Only through baptism, then, can children begin their spiritual regeneration, many Christians believe.
It is interesting that Golding's narrative contains no girls or women--no Eves to tempt man. Thus, it becomes apparent that Golding does believe that evil is inherent in man and not a result of outside forces; and, when the controls of civilization, which attempts the spiritual regeneration of man through religion and through moral laws, is removed, man regresses to his intrinsically degenerate nature.
The island, a virtual Garden of Eden, is invaded by "mankind's essential illness" that only Simon recognizes and the Lord of the Flies symbolizes. Finally, at the point that he is rescued, Ralph comprehends, weeping for the "end of innocence" acquired by the abandoned spiritual regeneration of his society.
The title "Lord of the Flies" is a Biblical one. It refers to Beelzebub (who is called Lord of the Flies), one of the seven princes of Hell. In literature, the term Beelzebub is often synonymous with evil and Satan. The theme of good vs evil is not only represented by the characters, but Golding believes that evil exists within each human heart. The "beast" of the island manifests itself in many ways. It is first an unsubstantiated fear, it is next manifested by the corpse of the parachutist and then a sow's head, and finally Simon metaphorically turns into a type of beast when he encouters and sow's head and freaks out.
The author's point is that all men are basically evil. It is not society that makes them evil. Evil exists in our hearts. By taking innocent children and putting them on a deserted island, far removed from grownups (society), Golding illustrates that eventually the evil within us will destroy us, even apart from the so-called evil influences of society. Man does not need society to destroy himself. He can do it pretty well all by himself. This is a Biblical theme because the Bible teaches that man is born into sin and the only redemption possible is through faith in God.
Really, this whole book is about this theme. You can see the theme in just about any interaction between Jack and Ralph or between the hunters and Piggy. This is especially true later in the book.
In this book, evil is represented mostly by Jack (as a representative of the hunters) and by Roger. Good is represented by Ralph and by Simon, in my opinion.
So I guess I would say that the best single example is when the hunters kill Simon. There, we are seeing that when there is no civilization, evil will eventually run wild and will kill the good. You can also see this in how Piggy is killed. Finally, remember that Ralph only survives this book because civilization (the naval officer) saves him.