What is the most important scene in To Kill a Mockingbird by Harper Lee?

It is hard to pick the most important scene in the novel. Of course, there are significant moments between Atticus and Scout. The trial, interactions with Boo, and the themes of race and class are all very important. Scout's discussion with Miss Maudie at the beginning of Chapter 10 ties into some of these issues. Scout recalls her father once telling her that it is a sin to kill a mockingbird. She asks Miss Maudie...

It is hard to pick the most important scene in the novel. Of course, there are significant moments between Atticus and Scout. The trial, interactions with Boo, and the themes of race and class are all very important. Scout's discussion with Miss Maudie at the beginning of Chapter 10 ties into some of these issues. Scout recalls her father once telling her that it is a sin to kill a mockingbird. She asks Miss Maudie about this. Miss Maudie replies: 

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. 

This is one of the more significant lessons in the book and is obviously where the title of the novel comes from. It is a sin to kill or harm anything or anyone who is innocent. The mockingbird does no harm and only provides music. Boo Radley and Tom Robinson are mockingbirds. Boo does not harm anyone and he proves to be generous and helpful throughout the novel. He covers Scout with the blanket when Miss Maudie's house is on fire and he saves the children in the end. Tom harms no one. His only "sin" was that he tried to help Mayella and got falsely accused in the process. It was sin that he was charged, convicted and killed. "To Kill a Mockingbird" is to harm the innocent.