"First of all," he said, "if you can learn a simple trick, Scout, you'll get along a lot better with all kinds of folks. You never really understand a person until you consider things from his point of view […] until you climb into his skin and walk around in it." (3.85-87)
Atticus's advice "to climb into someone's skin and walk around in it" is a little more Silence of the Lambs than the typical advice to walk a mile in someone's shoes, but the idea is the same: compassion is based on sympathy, on being able to put yourself in the other person's place and understand why they act the way they do even if you don't agree with it.
"This time we aren't fighting the Yankees, we're fighting our friends. But remember this, no matter how bitter things get, they're still our friends and this is still our home." (9.27)
If you're engaged in bitter warfare with someone, can you still be their friend at the same time? (Duh. That's why the word "frenemy" was invented.) But seriously—Atticus would say, sure can. You continue to treat them with a friend's respect, and you remember that they're part of a larger community that stays whole even if its parts are pulling in different directions.
"Scout," said Atticus, "when summer comes you'll have to keep your head about far worse things... it's not fair for you and Jem, I know that, but sometimes we have to make the best of things, and the way we conduct ourselves when the chips are down—well, all I can say is, when you and Jem are grown, maybe you'll look back on this with some compassion and some feeling that I didn't let you down." (11.53)
Sometimes it's kids rather than parents who just don't understand. Atticus knows that his behavior seems incomprehensible or just plain stupid from some perspectives, so he hopes Scout and Jem will be able to understand why he did what he did when they're older, even if they're too young to get it now. There's no shame in being an object of compassion.
Suddenly Mayella became articulate. "I got somethin' to say," she said.
Atticus raised his head. "Do you want to tell us what happened?" But she did not hear the compassion in his invitation. (18.165-166)
Mayella can't recognize Atticus's politeness or compassion. That shows just how different her world is from his—neither is something she's had any experience with, and so they're strange to her. Poor Mayella. Even our cold hearts almost feel sorry for her.
"Jem, see if you can stand in Bob Ewell's shoes a minute. I destroyed his last shred of credibility at that trial, if he had any to begin with. The man had to have some kind of comeback, his kind always does. So if spitting in my face and threatening me saved Mayella Ewell one extra beating, that's something I'll gladly take. He had to take it out on somebody and I'd rather it be me than that houseful of children out there. You understand?" (23.15)
Maybe Atticus really is so selflessly good that he can feel compassion even for Bob Ewell. Or maybe compassion really is based on a sense of superiority. Atticus can afford to be so generous because he knows he's so much better off than the Ewells will ever be, just because he was born a Finch instead of a Ewell. Or… both?
"There's one thing I truly believe, Gertrude," she continued, "but some people just don't see it my way. If we just let them know we forgive 'em, that we've forgotten it, then this whole thing'll blow over." (24.40)
While Atticus talks about seeing things through other people's eyes, Mrs. Merriweather is more concerned with people seeing it through her eyes. (Or trying on her skin. Ew.) Her insistence that the African-Americans need to be forgiven (for what?) shows that Mrs. Merriweather's compassion is so one-sided as to be hardly compassionate at all.
"Oh child, those poor Mrunas," she said, and was off. Few other questions would be necessary.
Mrs. Merriweather's large brown eyes always filled with tears when she considered the oppressed. "Living in that jungle with nobody but J. Grimes Everett," she said. "Not a white person'll go near 'em but that saintly J. Grimes Everett."
Mrs. Merriweather played her voice like an organ; every word she said received its full measure: "The poverty... the darkness... the immorality—nobody but J. Grimes Everett knows." (24.26-28)
Oh, sure—feel sorry for the poor "oppressed" Mruna, but not poor oppressed maid Sophy. While Mrs. Merriweather may talk about compassion, and believe that she herself is a compassionate person, actions suggest otherwise. It's easy to feel compassion in the abstract, but living it is much more difficult.
Jean Louise Finch (Scout)
[Jem] was certainly never cruel to animals, but I had never known his charity to embrace the insect world.
"Why couldn't I mash him?" I asked.
"Because they don't bother you," Jem answered in the darkness. He had turned out his reading light.
"Reckon you're at the stage now where you don't kill flies and mosquitoes now, I reckon," I said. "Lemme know when you change your mind. Tell you one thing, though, I ain't gonna sit around and not scratch a redbug."
"Aw dry up," he answered drowsily.
Jem was the one who was getting more like a girl every day, not I. (24.7-12)
If compassion is a girl's quality, then why have most of Scout's lessons on compassion come from Atticus? Maybe the larger cultural message that feelings=feminine trumps her personal experience. In any case, she's using the idea that "compassion" equals "girl" in order to assert that "girl" definitely does not equal "Scout."
I looked behind me. To the left of the brown door was a long shuttered window. I walked to it, stood in front of it, and turned around. In daylight, I thought, you could see to the post office corner. […]
Atticus was right. One time he said you never really know a man until you stand in his shoes and walk around in them. Just standing on the Radley porch was enough. (31.25-31)
Talk about talking things too literally: Scout actually stands on the Radley porch and imagines what Boo has seen over the last few years. And what Boo has seen—the life and times of Jem and Scout—has made him feel compassion for them. Are "seeing someone" and "imagining what someone else sees" different? What is it about seeing in particular that sparks compassionate feelings?
"Yes, suh. I felt right sorry for her, she seemed to try more'n the rest of 'em-"
"You felt sorry for her, you felt sorry for her?" Mr. Gilmer seemed ready to rise to the ceiling. The witness realized his mistake and shifted uncomfortably in the chair. But the damage was done. Below us, nobody liked Tom Robinson's answer. Mr. Gilmer paused a long time to let it sink in. (19.125-126)
Uh-oh. Why is Tom's compassion for Mayella such a problem? Well, feeling sorry for someone usually implies that you think they're worse off than you are—and in racially-divided Maycomb, for any African-American person to think he's superior to any white person is seriously messing with the order of things.