What purpose does each of the five factions serve in society?

As previously stated, the entire lives of the citizens in Divergent are determined by what faction they are in. The only freedom they are granted is the ability to choose their faction; but even then, their decisions are heavily influenced by the faction they grew up in. There is little social mobility; a person's life follows one of the predetermined roles in their respective faction. Amity are farmers and counselors, Erudite teachers, Abnegation run the government, Candor handle the law, and Dauntless are in charge of the city's security. Your leisure activities of choice correspond to those promoted by your faction, and you are meant to marry within the faction as well. Should you prove to not fit in the faction of your choice, you become factionless, below the faction members in status in every way, forced to live out in the dangerous recesses of the city. Much of the discourse in the novel comes from citizens dissatisfied by the way they are so rigidly placed into a caste, fighting to have more freedom than they have been given. But what will happen if they are successful? What would come next? Divergent illustrates the prevalent truth that when people are placed into immutable classes in such a way, there will always be those who are not content.

Each of the five factions serves an important role in maintaining the balance of nature. The role of the Dauntless is to protect society from potential threats where as the Abnegation was made to provide fair government to all factions. Amity was made to provide compassionate caretakers and counselors. The Candor faction provided the people with trustworthy and sound leaders in law. They are very truthful, sometimes to the point of being tactless. Erudite often go off to become knowledgeable teachers.