In To Kill a Mockingbird why is it important not To Kill a Mockingbird?

In Chapter 10 of "To Kill a Mockingbird" we are finally given the story behind the title of the novel. There is a metaphor that shows mockingbirds in a pure and innocent light. It is as if the mockingbird represents innocence and killing it represents the evils of the world. Scout recalls that the only time she ever heard Atticus say that something was a sin was when he said "Remember it's a sin to kill a mockingbird." She then asks Miss Maudie about this and Miss Maudie responds "Your father is right...Mockingbirds don't do one thing but make music for us to enjoy . . . but sing their hearts out for us. That's why it's a sin to kill a mockingbird." They are saying that the mockingbird is such an innocent creature that by killing it you commit terrible sin.