Represents Evil:  The beast is a kind of barbaric supernatural personality. In most cases, it exists in the heart of every human being. It is a symbol of potential evil and violence. The boys fear the beast, but only Simon realizes that they fear it because it exists within each of them. Simon is the one who knows the truth that there is no beast on the island. Simon's encounter with the Lord of the Flies represents this realization. It says, 

You knew, didn’t you? I’m part of you?

Savagery and Barbarism: Here, Jack is the manipulator. He uses the beast as a way of gaining and maintaining power. He uses the beast to unify the boys over a common fear. Jack presents himself as a strong leader who can protect the boys from threats.

If there were a beast, I’d have seen it. Be frightened because you’re like that – but there is no beast in the forest.

The Dark Side of Human Nature: The beast in the novel symbolizes the dark side of human nature. Simon is martyred for trying to bring them the truth. It reflects the cruel portion of human nature. 

In a more analytical sense, the beast is a symbolic representation of evil human nature in society. Through its depiction, Golding explores the darker aspects of human nature and the weak nature of civilization.