Humans find the potential for excellence in the city, but not without justice. Justice plays an important part in the ordering of the business and political associations in a city. There are two forms of justice: lawfulness and equality. Equality is giving one what one deserves. If one is exchanging goods, the character of justice is sure to pay what is fair, usually in the form of a currency. A just person does not steal or fight to come out ahead in a deal.
Lawfulness, the other definition of justice, is essentially a synonym for virtue. A lawfully just person is a virtuous person. This person can act unjustly, but he or she has developed an excellence of character in the virtues such that he or she is knows how to, and is able to act out of the right virtue at the right time in the right way.
The best person, the lawfully just person, actively participates in the politics of the city in order to legislate just and virtuous laws, and to lead the city as a just leader. He or she, of all citizens, is best prepared to educate the other citizens because of his or her grasp of justice, and is therefore obligated (and proportionally awarded) to give the citizens the potential to become good themselves.