The three most important themes in To Kill a Mockingbird are inequality, moral education and family. There are plenty of other themes we could go into, but these three are the most profound.
The inequality in the book starts from the very beginning of the novel. We see that there is inequality where Boo Radley is concerned. The whole town just gossips about him and his family. Atticus tries to put a stop to it, but to no avail. When Tom Robinson is accused of the crime, the whole town turns against him. Because he is a black man, there is no way he will ever get a fair trial in Maycomb. Atticus does everything he can and proves that Tom is innocent, but the jury and the town itself, convict him anyway.
Moral education is extremely important to Atticus. He tries his very best to teach Jem and Scout the rights and wrongs of morality. He tries to show them that you never judge someone until you know all the facts and you never treat someone badly just because of the color of their skin. He wants his children to have high morals, and the best way he can teach them this is to show them. He lives what he preaches and his children learn from him how to treat people.
The theme of family is one of the major themes of the novel. Although Jem and Scout fight sometimes and don't always see eye to eye on things, they are always there for each other. They might not always understand Atticus, but they have the most respect for him. Atticus will do anything for his children and will go to any length to make sure they are safe. Because he loves them so much, he teaches them how important it is to treat people fairly and with kindness.
"When they saw him, why he hadn't done any of those things...Atticus he was real nice." His hands were under my chin, pulling up the cover, tucking it around me. "Most people are, Scout, when you finally see them." He turned out the light and went into Jem's room. He would be there all night and he would be there when Jem waked up in the morning.
This quote sums up all the themes in the book. This one quote represents everything Atticus stands for and all that he has taught Jem and Scout.