Atticus and Miss Maudie are in the minority. They believe that people should not be judged by the color of their skin. They see the racism and blindness that are endemic to Maycomb and want to change it. A few others see it, too, such as Heck Tate and Judge Taylor. They all know that it will take time, effort, and sacrifice to make gains. More importantly, they are courageous and willing to put their hearts into it.
The best way to proceed is to give examples of what they stand for:
First, as the title suggests they believe that it is a "sin" to kill a mockingbird. They see people like Tom Robinson as mockingbirds. They also see Boo Radley as a mockingbird by the end of the story. Here is what Miss Maudie says:
“Your father’s right,” she said. “Mockingbirds don’t do one thing but make music for us to enjoy. They don’t eat up people’s gardens, don’t nest in corncribs, they don’t do one thing but sing their hearts out for us. That’s why it’s a sin to kill a mockingbird.”
Second, they all believe that people have blindspots. Here is what Atticus say to Jem over dinner.
Atticus placed his fork beside his knife and pushed his plate aside. “Mr. Cunningham’s basically a good man,” he said, “he just has his blind spots along with the rest of us."
Jem spoke. “Don’t call that a blind spot. He’da killed you last night when he first went there."
The best quote on this topic comes from Miss Maudie. Let me quote her in full:
“We’re the safest folks in the world,” said Miss Maudie. “We’re so rarely called on to be Christians, but when we are, we’ve got men like Atticus to go for us."
Jem grinned ruefully. “Wish the rest of the county thought that.” “You’d be surprised how many of us do."
“Who?” Jem’s voice rose. “Who in this town did one thing to help Tom Robinson, just who?"
“His colored friends for one thing, and people like us. People like Judge Taylor. People like Mr. Heck Tate. Stop eating and start thinking, Jem. Did it ever strike you that Judge Taylor naming Atticus to defend that boy was no accident? That Judge Taylor might have had his reasons for naming him?"
This was a thought. Court-appointed defenses were usually given to Maxwell Green, Maycomb’s latest addition to the bar, who needed the experience. Maxwell Green should have had Tom Robinson’s case.
“You think about that,” Miss Maudie was saying. “It was no accident. I was sittin‘ there on the porch last night, waiting. I waited and waited to see you all come down the sidewalk, and as I waited I thought, Atticus Finch won’t win, he can’t win, but he’s the only man in these parts who can keep a jury out so long in a case like that. And I thought to myself, well, we’re making a step—it’s just a baby- step, but it’s a step.”