| Quote #1
Roses. Not virgins like dogwood, milkweed. I said I have committed incest, Father I said. Roses. (2.4)
Thinking about the flowers in Caddy’s wedding bouquet sends Quentin into a frenzy. In his mind, roses aren’t "virginal" flowers – in other words, Caddy’s not a virgin when she gets married. To save himself from this thought, he decides to confess that he’s committed incest with Caddy, even though he hasn’t.
| Quote #2
That Christ was not crucified: he was worn away by a minute clicking of little wheels. That had no sister. (2.2)
Note how Quentin’s sentences start with "that" – as if he’s continuing a single thought. One interpretation of this passage could be that Quentin sees himself as a Christ-like figure – but even then, he can’t fully identify with Christ, because Christ never had to deal with the type of feelings that Quentin has for Caddy.
| Quote #3
Because if it were just to hell; if that were all of it. Finished. If things just finished themselves. Nobody else there but her and me. If we could just have done something so dreadful that they would have fled hell except us. (2.10)
Quentin desires a sin so bad that everyone would leave him alone with Caddy. As he thinks, it’s better than the mess of human relationships he has to deal with now.