"Musical Training is a more potent instrument than any other, because rhythm and harmony find their way into the secret places of the soul." ~Plato from "The Republic" (Greek: Πολιτεία, Politeia) a Socratic dialogue written by Plato around 380 BC concerning the definition of justice and the order and character of the just city-state and the just man.
Socrates: "[...] injustice is never more profitable than justice." Glaucon: "The best is to do injustice without paying the penalty; the worst is to suffer it without being able to take revenge. Justice is a mean between these two extremes. People value it not because it is a good but because they are too weak to do injustice with impunity."
Read it for Philosophy, reading it again when classes are over The Republic by Plato - The Republic is Plato's most famous work and one of the seminal texts of Western philosophy and politics. The characters in this Socratic dialogue - including Socrates himself - discuss whether the just or unjust man is happier. (Bilbary Town Library: Good for Readers, Good for Libraries)
The four cardinal virtues are wisdom, courage, moderation and justice. Plato wrote about these virtues in the "Republic," a Socratic dialogue on political theory. Other philosophers have argued that the four virtues provide the basis for all aspects of moral character.