Socrates' brief conversation with Cephalus is only apparently innocuous; this exchange actually foreshadows several aspects of the just life and the establishment of the just state that will be attempted in the duration of the argument for the Republic.
During Plato's time, Greek thinkers had already established the idea that the good man possesses four cardinal virtues: courage, temperance, justice, and wisdom. In Cephalus, Socrates seems to have met a man who, through the experience of age, seems to have achieved the virtue of courage in that one's denial of the passions (one of which is boundless sexual appetite) requires a kind of courage perhaps surpassing physical courage in combat; in learning to temper his passions, he has achieved temperance. At the same time, Cephalus seems to have attempted to achieve justice in that he tells the truth and repays his debts, and he has tried to think his way through to achieving right conduct and, perhaps, the good life. But as soon as it becomes clear that Socrates has an intricate philosophical subject in mind (the attainment of justice and the establishment of justice for all), Cephalus excuses himself from the conversation: It is plain that he does not pretend to be a philosopher (to love knowledge for its own sake), and, having achieved knowledge, to have achieved wisdom.
Socrates has made it plain in the dialogue that we have not achieved justice because we have not even been able to define justice. Cephalus, in retiring from the conversation in order to sacrifice to the goddess, may be said to be rendering a kind of justice to the gods. But in the dialogue, it is clear that we cannot have achieved justice because we have not thus far been able even to define justice.
