What are quotes in To Kill a Mockingbird that support the duality of good vs evil—specifically where Atticus represents good and Bob Ewell evil?
Most of the examples showing the duality between good and evil—Atticus Finch vs Bob Ewell—can be found in chapter 23. There is also one in chapter 3.
When Bob Ewell spits in his face, all Atticus just says,
"I wish Bob Ewell wouldn't chew tobacco" (217).
This shows that, even though Bob Ewell is low enough to spit in someone's face, Atticus is big enough not to let it phase him. When discussing the issue with his son, Jem, Atticus makes sure to teach an important lesson:
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 (218).
Knowing Ewell's tendency to beat his daughter, Mayella, Atticus does not mind taking the brunt of Ewell's aggression if it saves her from another beating. There is nothing but goodness in this lesson from Atticus, whereas the only lessons Bob Ewell teaches his children is starvation and survival of the fittest. What Atticus doesn't tell his children about the face-off with Ewell is what Miss Stephanie reveals,
Mr. Ewell was a veteran of an obscure war; that plus Atticus's peaceful reaction probably prompted him to inquired, "Too proud to fight, you ni****-lovin' bast*rd?" Miss Stephanie said Atticus said, "No, too old," put his hands in his pockets and strolled on. Miss Stephanie said you had to hand it to Atticus Finch, he could be right dry sometimes (217).
Miss Stephanie calls Atticus dry, but it takes a strong man to walk away from someone who tries to humiliate him in public. Not only that, but Atticus doesn't show any pride in dismissing Ewell. He is humble and peaceful at all times, no matter what happens.
Another part that shows Atticus discussing the evils of Bob Ewell with his daughter is in chapter three. Scout wonders why Burris Ewell doesn't have to go to school. Atticus explains Mr. Ewell isn't the best father around, so the community allows the family some concessions. One concession is they allow Ewell to hunt out of season, which Scout says is bad. Atticus responds,
"It's against the law, all right... but when a man spends his relief checks on green whiskey his children have a way of crying from hunger pains. I don't know of any landowner around here who begrudges those children any game their father can hit (31).
With this example, Atticus shows how evil Ewell is to make his children go hungry. Later, we learn Bob Ewell doesn't even call a doctor for his children when they are sick and suffering. They are also very unclean and live in an impoverished environment. Scout, who has a very dutiful and loving father, does not suffer or fear a beating each night in her home. The contrast between Atticus and Bob Ewell behave as parents is drastic, just like good vs. evil.