Conflicts of race and social belonging are important in this book. There are so many quotes you might consider.
"Scout," said Atticus, "nigger-lover is just one of those terms that don't mean anything—like snot-nose. It's hard to explain—ignorant, trashy people use it when they think somebody's favoring Negroes over and above themselves. It's slipped into usage with some people like ourselves, when they want a common, ugly term to label somebody." ch 11
Lula stopped, but she said, "You ain't got no business bringin' white chillun here—they got their church, we got our'n. It is our church, ain't it, Miss Cal?" ch 12
"It's right hard to say," she said. "Suppose you and Scout talked colored-folks' talk at home it'd be out of place, wouldn't it? Now what if I talked white-folks' talk at church, and with my neighbors? They'd think I was puttin' on airs to beat Moses." ch 12
"There's four kinds of folks in the world. The ordinary kind like us and the neighbors... the Cunningams... the Ewells... and the Negroes."ch 23