Discuss the importance of the book's title. How does Harper Lee use this extended metaphor and what is its effect?

Scout and Jem receive air rifles for Christmas in chapter nine. In chapter ten, as the kids start using the rifles, Atticus says the following:

"I'd rather you shot at tin cans in the back yard, but I know you'll go after birds. Shoot all the bluejays you want, if you can hit 'em, but remember it's a sin to kill a mockingbird" (90).

This is where the book's title comes from. Specific elements in this passage foreshadow a motif, or extended the metaphor that can be applied to characters and events that Scout encounters in the text. First, the children's rifles symbolize power and strength over birds who cannot defend themselves against them. The rifles can be compared to white privilege, prejudice, gossip, or anything that hurts a weaker person.

Next, the symbolism from the title of the book and Atticus's rule create a repeated lesson capable of being applied to different characters and situations. For example, Tom Robinson and Boo Radley represent mockingbirds in Maycomb. Both are weaker compared to the majority of people in town. Tom Robinson is weaker socially, financially, and politically because he is African American. Boo Radley, on the other hand, is white, but he is weaker socially and politically because he is shy, socially awkward, and probably deals with a mental disability or phobia. Both men are treated disrespectfully in the novel. The lesson behind these two men's stories suggests that just because someone is different or weaker, doesn't make it right for people who have many opportunities and privileges to take advantage of them through gossip, in social circles, with finances, or in a court of law.  

This is not a coincidence. Harper Lee specifically applies the extended metaphor of the mockingbird to drive home the main idea and theme of the novel. Without the link back to the title and the mockingbird, the lesson about how stronger people tend to take advantage of, or show prejudice against, the weak may not have had the intended and powerful effect that it has had for fifty years. That is to say, the title and Atticus's rule help readers remember mockingbirds like Tom Robinson and Boo Radley. Then, if they ever encounter anyone weaker than themselves, they will share compassion and kindness rather than rumors, malicious intent, or violence.