It's a Sin to Kill a Mocking Bird.

 "Shoot all the blue jays you want, if you can hit em', but remember its' a sin to kill a mockingbird."

Mockingbird

  Boy about Jem's age with an air-rifle

This was said by Atticus Finch to Jem when he first got his air-rifle. It was the first time Scout had ever heard her father say something was a sin. Miss Maudie later explained to Scout that it was sinful because mockingbirds didn’t cause harm to anyone. They simply made beautiful music for us to enjoy. I believe this is a very wise quote because it can apply to many things in life. If someone or something is innocent and hasn’t done anything wrong, it would be cruel to do anything bad to them. There were multiple metaphorical “mockingbirds” in the book as well. Tom Robinson is an excellent example. Tom was never rude or outspoken to anyone. Most importantly, he never raped Mayella Ewell. When Mayella bluntly accused him of this in court, it was like she was shooting a mockingbird. At the end of the book, Scout finally understands this concept when Boo Radley saves her and Jem from Bob Ewell. If they exposed Boo to the public as a hero, his privacy would be invaded and his life would never be the same. In a way, it would be like saying they didn’t appreciate what he did. The whole idea of it being a sin to kill a mockingbird should be practiced by everyone. It’s bad enough when people are mean to each other, but it’s absolutely cruel to be mean to someone who has never done anything bad to you.