How we cite our quotes:
Bodily desire, like a morass, and adolescent sex welling up within me exuded mists which clouded over and obscured my heart, so that I could not distinguish the clear light of true love from the murk of lust. (II.2.1)
We've got two contrasting ideas here that help elucidate one another: love and lust. Augustine's word choices ("mists," "clouded," "murk") tell us that lust is an unclear, confusing, chaotic thing, while love is clear, bright, and full of sunshine and rainbows. By separating love and lust, Augustine makes a distinction between the wants of the body and the wants of the soul—and we have no doubts about which wants are more important to Augustine.
This was the age at which the frenzy gripped me and I surrendered myself entirely to lust, which your law forbids but human hearts are not ashamed to sanction. (II.2.3)
Ah, puberty… or, as Augustine calls it, "the broiling sea of my fornication" (II.2.1). Same difference. Now, the problem is that people generally like sex, and when people like something, they will find reasons to do it. So that's what Augustine means when he says that "human hearts are not ashamed to sanction" sex. Again, we're seeing a tension between earthly things (in this case, laws) and spiritual ones.
I went to Carthage, where I found myself in the midst of a hissing cauldron of lust. (III.1.1)
Sound kind of familiar? This line appears in T.S. Eliot's poem "The Waste Land"—only the translation he uses reads "To Carthage then I came". Augustine finds himself in the big city, and if sex was an issue before, in his little hometown, boy is it everywhere now. Carthage comes to represent vice, especially of the lustful variety. Also, remember way back in Book I.13, when Augustine talks about how much he loves the character Dido because she killed herself for love? Well, she also happened to be from Carthage. Just putting that out there.