How we cite our quotes: Stephanus pagination (the standardized way in which every text of Plato is divided). Every edition and translation will have this pagination in the margins.
Quote #1
"So long as I do not know what the just is, I shall hardly know whether it is a virtue or not and whether the one who has it is unhappy or happy." (354c)
Big Problem Alert. Socrates is pretty sure that if you don't know what justice means, you don't know squat. Without a basic definition of justice, Socrates can't begin to evaluate whether it's good or not.
Quote #2
"And this, then, is the genesis and being of justice: it is a mean between what is best—doing injustice without paying the penalty—and what is worst—suffering injustice without being able to avenge oneself." (359a)
Instead of attributing any moral value to justice, Glaucon's formulation presents it as a cowardly compromise for those afraid of being the victims of injustice. Glaucon is hopeful, and so are we, that Socrates can find a good argument against this definition.
Quote #3
"...no one is willingly just but only when compelled to be so." (360c)
In another bleak assessment of justice, Glaucon again presents himself as the devil's advocate, coming up with a very negative idea to provoke Socrates into a persuasive defense. Playing the devil's advocate is a good way to get someone (or yourself) to consider objections to a point you're making; it can help you cover all the bases and make sure your reasoning is secure.