For Plato, the good state is the just state.
When you have the Rulers characterized by wisdom, the Guardians characterized by courage and the Artisans characterized by temperance/moderation, you then have justice.
Trichotomy of Mind/Soul/Appetites. Wisdom/Courage/Temperance, relatively. When the person is in balance, he is just, therefore good.
There is a clear analogy between the just state and the just man.