his statement by saying that mockingbirds cause no harm and simply make beautiful music for people to enjoy. The metaphorical meaning of Atticus's lesson regarding mockingbirds concerns the importance of defending and supporting innocent, vulnerable beings. Throughout the story, severalcharacters are considered symbolic mockingbirds because they share many similar attributes to the pleasant, defenseless birds.

The two most notable symbolic mockingbirds are Tom Robinson and Boo Radley. Both characters are portrayed as innocent, compassionate individuals, who suffer from prejudice and rely on the protection of others. Atticus lives his truth and behaves as the consummate role model by valiantly defending Tom Robinson in front of a racist jury. Similar to defenseless, vulnerable mockingbirds, Tom is susceptible to the community's dangerous racism and tragically becomes the victim of racial injustice.

Boo Radley is also discriminated against by the community for his reclusive lifestyle. After saving Jem and Scout's life, Sheriff Tate exercises discretion and follows Atticus's lesson by concealing Boo's heroics and protecting him from the harmful community limelight. When Atticus asks Scout if she understands Sheriff Tate's reasoning, she answers by saying, "Well, it’d be sort of like shootin' a mockingbird, wouldn’t it?" Overall, Atticus's lesson about mockingbirds can be metaphorically applied to the importance of defending and supporting vulnerable individuals, which is a prominent theme in the story.

Like many contemporaneous Southern parents, Atticus has given air-rifles to his children. But Atticus, being Atticus, wants Jem and Scout to use their guns responsibly. The last thing he wants is for them to start going round indiscriminately shooting innocent creatures such as mockingbirds.

Mockingbirds are completely harmless animals; they never cause anyone any bother. They just sit in the trees all day, sweetly singing their song. That's why it would be a sin to kill one of them, as Miss Maudie helpfully explains.

As the story develops we begin to realize that as well as the literal mockingbirds who live in the trees, Maycomb also has more than its fair share of figurative mockingbirds. There are many innocent souls who never do anyone any harm, but are nonetheless marginalized and despised by society for all kinds of different reasons.

The main case of the metaphorical mockingjay would be Tom Robinson, an African-American tried and convicted on a trumped-up charge of raping a white woman for no other reason than racism.

Then there's Arthur "Boo" Radley, who is stigmatized by the community as some kind of boogeyman. His reputation sticks despite the fact that there's no hard evidence that he's ever harmed a living soul. All kinds of urban legends have accrued to his name over the years, but there's nothing to suggest that he, like Tom Robinson, is anything other than one of life's mockingbirds.

When Jem and Scout receive air-rifles, Atticus tells them "it's a sin to kill a mockingbird." It is Miss Maudie that explains to Scout that "Mockingbirds don’t do one thing but make music for us to enjoy." Mockingbirds symbolize innocence in the story. Consider Boo Radley. In the beginning of "To Kill a Mockingbird," Scout and Jem are terrified of Boo. They believe the tales of neighbors that blame Boo for many unfortunate events. However, at the end of the novel, Boo saves the lives of Jem and Scout. Sheriff Tate believes that Boo deserves his privacy and doesn't wish to involve him in the explanation of Bob Ewell's death. Agreeing with the sheriff, Scout says that to involve Boo would be "sort of like shootin' a mockingbird." Instead of the horrible person he was believed to be, Boo is actually a kind and and generous man.

Another "mockingbird" is Tom Robinson. Tom provides an act of kindness and is then accused of rape by the young woman he helps. In racist Maycomb County, Tom doesn't stand much of a chance in court. Atticus is able to point out many discrepancies and contradictions in the testimony of Bob and Mayella Ewell. However, even with the knowledge that Tom only has the use of one arm, the jury finds him guilty because of the color of his skin.

When Atticus tells his children that "it is a sin to kill a mockingbird," he does not give much explanation. Scout asks Miss Maudie, and she explains his reasoning by saying that all mockingbirds do is provide beautiful music. They do not harm anyone, they don't bother anyone, and they "sing their hearts out for us." As the previous poster stated, many characters in the book are "mockingbirds." Boo Radley is perhaps the strongest example because he wants nothing more than to keep to himself. When he saves Jem and Scout from Bob Ewell, he risks becoming the town hero, which is something he does not want. If Atticus and the rest of the people present at the time told the truth about what Boo did, they would be, essentially, killing a mockingbird. Boo did only good for them and they would turn his life into something he does not want.

In chapter 10, when Jem and Scout get their air rifles, Atticus is very honest about his feelings on what they can and can not shoot at. 

"I'd rather you shoot at tin cans in the back yard, but I know you'll go after birds. Shoot all the blue jays you want, if you can hit'em, but remember it's a sin to kill a mockingbird." That was the only time I ever heard Atticus say it was a sin to do something, and I asked Miss Maudie about it. "Your father's right," she said. "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, the only thing they do is sing their heats out for us. That's why it's a sin to kill a mockingbird."

Atticus just tells them it is a sin to kill a mockingbird, and Scout gets her answer as to why, from Miss Maudie. A mockingbird is just there for us to listen to their sweet music, and that is all. Later on in the story, Boo Radley is compared to a mockingbird. Boo saves Jem and Scout and Atticus knows that if the people of the town found out about it, they would turn Boo into the town hero, and that is the last thing Boo would want. Scout realizes this, as well, at the end of the book. She tells Atticus that if they told what Boo did, it would be like killing a mockingbird. 

In Harper Lee's To Kill a Mockingbird, the kids get air-rifles from Uncle Jack for Christmas. Uncle Jack gives them basic instruction about how to use the air-rifles, telling them that Atticus isn't much interested in guns. (This is an ironic statement based on the need of Atticus' excellent marksmanship when the threat of a rabid dog enters the neighborhood.)

Atticus gives the children instructions about what they can and cannot shoot.

I'd rather you shot tin cans in the backyard, 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.

(*Killing bluejays probably reflects the predatory nature of bluejays to attack and kill other birds.) It is actually Miss Maudie that explains Atticus' stand on mockingbirds.

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 reflects a central theme of the story: symbolically, Tom Robinson and Boo Radley are seen as mockingbirds in the story: neither one has ever caused harm to anyone, and yet they are both victimized. Tom is tried and convicted for a crime he did not commit, and Boo has been victimized by his family—first by his father and then his brother, so he is nothing but a shadow of the young man he once was, but almost a ghost.

The idea behind protecting mockingbirds is that no harm should come to those who cause no harm.