The Republic

I'm sitting in my Political Heritage class right now. The professor is talking about Socrates in the Republic. Not quite sure that I'm a big fan of Socrates. He asserts that he's not smarter than anyone, but then he asks these questions that are infuriatingly condescending and take us on these tangents that in reality have nothing to do with the nature of justice. Unfortunately, the Republic is merely Plato's interpretation of Socrates, so it's entirely possible that Socrates isn't actually that infuriating.
Additionally, I hate that in book 2 they take a dreadful tangent to see justice 'writ large'. I enjoyed(on the 'it made me think' level) the example that Glaucon/Adeimantus put forth and I don't see why they all of a sudden start making up this imaginary city and go into an incredible amount of detail about the Gaurdians. I fail to see the connection to the discussion of justice.
If we take away all the temporal advantages of justice, is it intrinsically good? I fear that the answer is no. Without the addition of the external Good, there are no benefits to being just. Whereas, being injust is only bad when we add the external Good. If there were no divine consequences for our actions, then what would the benefit of being just be? Fortunately for me(so that I don't go around being unjust), there are consequences.