What does Glaucon want to demonstrate by giving two people rings?

In the Republic, Glaucon uses the story of the Ring of Gyges to illustrate the idea that people are only good when they are afraid of the consequences of their actions. He compares two men, one of whom is given the ring and the other of whom is not. The man who has the ring is free to do whatever he wants without being punished, while the man who does not have the ring must follow the rules of society in order to avoid punishment. Glaucon argues that the man with the ring will be more likely to behave unjustly, because he knows that he will not be punished. This story is meant to show that people are naturally selfish and will only behave morally if they are forced to do so.