What theme does the subplot involving boo radley reinforce

Boo Radley symbolizes the mockingbird, an animal which, according to Atticus, is a creature that does harm to no one and simply want to bring pleasure to others. This is shown when he saves the children from the attack and when he leaves out presents for them. The title of the novel, To Kill A Mockingbird, also refers to how people were expecting the worst out of Boo Radley when they didn't know who he really was and only knew rumors about him.