It can be argued that the most prominent theme in 'To Kill A Mocking Bird' is prejudice. It is directed towards groups and individuals in the Maycomb community. Prejudice is linked with ideas of fear and injustice.
There was surely no nation in the world that holds "racism" in greater horror than does the United States at the time. Fear and paranoia led to the Whites believing that the Blacks desired all the whites had, including their women.
A mockingbird is a harmless bird that makes the world more pleasant. In To Kill A Mockingbird by Harper Lee, the mockingbird symbolizes Boo Radley and Tom Robinson, who were both peaceful people who never did any harm.
Boo Radley went through his life never wanting to hurt a fly. He left gum, pennies, and dolls for Scout and Jem. He sewed Jem's pants and left them on the fence so Jem could get them easily.
He also saved Scout's and Jem's lives while risking his own. Boo was a gentle person. Throughout the novel, Scout, Jem, and Dill are curious about the "mysterious" Boo Radley because he never comes outside from his house or speaks with anyone in the neighborhood. The children are afraid of him because of all the stories they hear about him from the people in Maycomb. For example, Miss Stephanie tells the children that while Boo was sitting in the living room cutting a magazine, he "drove the scissors into his parent's leg, pulled them out, wiped them on his pants, and resumed his activities." After hearing stories like these, the children consider him to be evil.
By the time, they assume more about Boo because he never goes outside. Boo Radley becomes a game for the children and they talk about Boo Radley scenarios...