How we cite our quotes: (Part.Chapter.Paragraph.)
Quote #4
How often the priest had heard the same confession—Man was so limited he hadn't even the ingenuity to invent a new vice: the animals knew as much. (2.1.331)
In Catholicism, sin is a sign of weakness, powerlessness, and limitation. The more you sin, the more you are possessed by sin. It becomes a bad habit, like leaving dirty laundry on the floor, texting while talking to people, or picking your nose. Ewwwww.
Quote #5
What an unbearable creature he must have been in those days—and yet in those days he had been comparatively innocent. That was another mystery: it sometimes seemed to him that venial sins—impatience, an unimportant lie, pride, a neglected opportunity—cut you off from grace more completely than the worst sins of all. Then, in his innocence, he had felt no love for anyone; now in his corruption he had learnt… (2.3.173)
Some more background: Catholic moral theology distinguishes between venial sins and mortal sins. The first are the kinds of wrongs that are minor and easily passed with an apology. The second are the evils that severely injure the relationship one has with God and necessitate major repairs (contrition, confession). The priest believes he's in a state of mortal sin and therefore likely cut off from God and the hope of heaven; however, he also senses that he's a better person now. He isn't rejecting the Catholic understanding of sin, but recognizing that such strict distinctions don't quite capture the mystery.
Quote #6
"Lust is not the worst thing. It is because any day, any time, lust may turn into love that we have to avoid it. When we love our sin then we are damned indeed." (3.1.109)
This statement helps us understand why the priest believes himself damned. He can't bring himself to be sorry for his sin of fornication because he loves what his sin brought into the world—his child. He doesn't think he can love his child and hate the means that gave her life. Do you think he's conflating the two?