Atticus replies, "I'm simply defending a Negro-his name's Tom Robinson. He lives in that little settlement beyond the town dump. He's a member of Calpurnia's church, and Cal knows his family well. She says they're clean-living folks. Scout, you aren't old enough to understand some things yet, but there's been some high talk around town to the effect that I shouldn't do much about defending this man" (83). When Scout pushes Atticus to explain why he's defending Tom, Atticus states, "For a number of reasons.The main one is, if I didn't I couldn't hold up my head in town, I couldn't represent this county in the legislature, I couldn't even tell Jem not to do something again" (83). Atticus warns Scout that there is going to be a lot of ugly talk about him and the case over the course of the trial which will take place during the coming summer. Scout still does not understand why Atticus agreed to take the case:
"Atticus, are we going to win it?"
"No, honey."
"Then why-"
"Simply because we were licked a hundred years before we started is no reason for us not to try to win," Atticus said (84).
With that, Scout agrees not to fight over the case again.
Hope this helps!