How does the story tie into the title, To Kill A Mockingbird?

One of the major themes of the novel very closely ties in with the title. In Chapter 10, Atticus tells Jem and Scout, “remember it’s a sin to kill a mockingbird.” As Miss Maudie later explains to Scout,

“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.”

Two characters are symbolic of the mockingbird: Tom Robinson and Boo Radley.

In Tom’s case, we see him unjustly convicted of a crime that he did not commit. He is a kind, generous person, who, as Atticus puts it, “had the unmitigated temerity to ‘feel sorry’ for a white woman,” and he ultimately pays the price for this feeling with his life. Though his only intention is to help Mayella, he is treated cruelly for his kindness.

In Boo’s case, he is spared being the 'killed mockingbird' as Heck Tate protects him from being subjected to the Maycomb community after he saves Jem and Scout from Bob Ewell. After being shut up for so long, Boo does not want to be part of the community, and he will be pulled into the limelight if his actions are revealed.

“To my way of thinkin’, Mr. Finch, taking the one man who’s done you and this town a great service an’ draggin’ him with his shy ways into the limelight – to me, that’s a sin. It’s a sin and I’m not about to have it on my head. If it was any other man it’d be different. But not this man, Mr. Finch.”

Therefore, Mr. Tate will state that Bob Ewell fell on his knife during the struggle to protect Boo.  At the end of the novel, even Scout has come to the realization that revealing the details of their struggle in the woods would put Boo into the public eye, and “it’d be sort of like shootin’ a mockingbird, wouldn’t it?”

Throughout the experiences of the novel, Scout has learned of the inherent innocence both Tom and Boo have and has become able to determine that they are not deserving of the treatment they are given by the society around them.