What is the theme for Chapter 21?
Chapter 21 shows us the children watching the end of the trial, waiting for the verdict, finally hearing the guilty verdict, and then recognizing and participating in the admiration of the African Americans for their father. If they didn’t understand before, they certainly learn now what a hero their father is. Probably the most important sentence in the chapter occurs at the end when Scout says about the trial, “it was like watching Atticus walk into the street, raise a rifle to his shoulder and pull the trigger, but watching all the time knowing that the gun was empty.” Scout alludes to when Atticus shot the mad dog, and now we clearly know what that dog represents, which is racism. Then, when the madness staggered frothing down the street, Atticus killed it. Here, he raises his rifle, which is the law, but finds it powerless. The theme that emerges is that difficulty to eliminate racism, that it will take more than a round in the courts to do so.
In Chapter 21, the theme of the mockingbird comes to fulfillment.
Atticus has told the children that it is a sin to kill a mockingbird because a mockingbird never causes harm to anyone else. In Chapter 21, Tom Robinson is convicted of rape despite Atticus's efforts to save him. A great injustice has been committed, because, like the mockingbird, Tom Robinson has not done anything wrong, but he is judged to be guilty because of the color of his skin.