Seeing [Ray] like this—white-haired and vulnerable, a snoring corpse—I was filled with an unexpected sympathy for the guy. (11.37)
It's easy to feel compassion for someone when they're basically harmless. If Ray were still able to scream, yell, abuse, and torment, Dominick probably wouldn't be having these fluffy feelings for his stepfather.
"When you say, 'I know that,' do you mean you understand it intellectually or that you can feel the fear and frustration as he must feel it?" (15.290)
Dr. Patel tries to get Dominick to dig a little deeper, past understanding, and try to get to true empathy.
"I'm only attempting, as much as possible, to map your brother's past and present realities. To become him, as it were—try on his skin." (15.307)
Dr. Patel doesn't just talk the talk, she walks the walk. She's not only trying to get Dominick to empathize with Thomas, she's trying to do the same herself. She isn't just scribbling notes in a notebook, she's trying to understand.
"How?" […] "by sharing your own remembrances of the past." (15.309)
Dr. Patel also wants to empathize with Dominick, and maybe get him to understand himself a little bit better in the process.
"You have my sympathy. And my gratitude. […] For sharing that information with me. I know you are a private person, Mr. Birdsey. Thank you for trusting me." (15.331, 15.333)
A big part of understanding is trust. In order for Dominick to find someone that understands him, he has to first trust them enough to actually open up.
"The stream of memory may lead you to the river of understanding. And understanding, in turn, may be a tributary to the river of forgiveness." (22.350)
This is kind of a cheesy metaphor, but it's a good one. It shows that the journey to forgiveness is a journey, and while sometimes you can just go with the flow, sometimes you also need to take control and alter your own course to go down the right path.
It disarmed me—Ray's verbalizing his struggle over what Thomas had done. (26.55)
Dominick is usually too busy being angry with Ray to try to understand him, but just as Dominick struggles with how he treated Thomas over the years, Ray does the same thing. He just internalizes it more.
The key to peace within my soul, he said, was to cast aside my bitterness and resentment. (41.161)
Rage runs in the family. This is advice given to Dominick's grandfather by a priest, and although Domenico was never able to let go of all this anger, Dominick, by reading his grandfather's memoir, learns how important it is and tries to do it himself.
It felt weird that first time—unnatural—lathering him up, holding him by the chin and scraping the stubble off his neck, his slack cheeks. (46.146)
The shaving scene marks the moment when Dominick really forgives Ray. If he had needed to shave Ray as a teenager, he probably would have slit the man's throat with the blade.
She watched it swing, pendulum-like, before her—watched the reversal of the dark magic she had witnessed long, long ago. "Forgive me," I whispered. (47.290)
We're not sure why Dominick is asking Prosperine for forgiveness. Is it so he can rest better, knowing she has forgiven his grandfather, or is it so she can let it go?