A little too much anger, too often or at the wrong time, can destroy more than you could ever imagine. (1.1.12)
Ames would know. He's seen what anger does—in fact, he's seen it sever the bonds of parents and children. That's serious business.
When the Lord says you must "become as one of these little ones," I take him to mean you must be stripped of all the accretions of smugness and pretense and triviality. (1.2.57)
Children just are who they are. They play without trying to hide their desires. In that way, you could say they're more authentic than adults.
I believe my father was trying to cover up for Cain, more or less. (1.7.24)
Cain is the first murderer in the Bible, and he's frequently used as a symbol for primeval murder or for the original murderous impulse. Even more than Adam and Eve, he's a symbol for the presence of sin in the world. Ames is saying that his father wanted to get rid of this sinful, murderous impulse—the kind of thing that leads people to go to war, for example.
I think that fierce anger against him was one of the things my father felt he truly had to repent of. (1.7.54)
The anger in the Ames family, which Ames shares, has alienated father and son. It's destroyed solidarity—and in Christian theology, that's a clear sign of the sinful nature of this particular emotion.
These people who can see right through you never quite do you justice, because they never give you credit for the effort you're making to be better than you actually are, which is difficult and well meant and deserving of some little notice. (1.7.90)
Jack has a way of seeing into someone and knowing if they're honest. Ames worries that this ability to understand people's honesty might make people seem worse than they are to Jack. Jack detects the dishonesty in people, but he doesn't necessarily detect others' desire to do better.
My father hated to believe he was the man my grandfather shot, but he did believe it. (1.7.119)
Ames's father can't have closure, because he can't either prove or disprove his own father's guilt. He's probably right, but he still judges himself harshly for assuming the worst.
"I never did forgive myself not going out there to look for him." (1.7.123)
Ames's father could have gone looking for the soldier his own father had shot, and he might have saved the soldier's life by doing so. He regrets this "sin of omission" (that's a sin you commit by not doing something).
There is never just one transgression. There is a wound in the flesh of human life that scars when it heals and often enough never seems to heal at all. (1.8.20)
Here, sin is visualized not as a transgression but as a wound. In other words, we do sinful things because we are broken, not because we're naturally bad. A wound calls for healing, not punishment.
"…the hotel clerk where we got a room charged me a good deal extra for turning a blind eye, or words to that effect." (2.21.55)
Not all that long ago, it was illegal for an unmarried couple to cohabit, or live together. It was also illegal in many places for people of different races to marry. "Good" people took advantage of this law and taboo: basically, they could justify their prejudices by just saying they were following the law.
"…the police came to speak with us, to mention that law about cohabitating." (2.21.68)
Cohabitation refers to unmarried people living together—a common practice nowadays, but much less so in Ames's time. It's hard to imagine police pursuing this matter now, but back in those days, people really got up in arms about it.