One theme deals with the idea of justice. What is fair in the world? Is the world fair at all? Are justice and fairness even the same things?
The book also concerns itself with the Civil Rights Movement and racism. The book deals with racism not only between white and black people, but between people of mixed race.
The third major theme of the novel deals with God and religion, and its place in society. Jefferson is trying to understand his faith and his relationship with God throughout the novel.
The main theme is basically Justice and Injustice.