Cultural constructs and change
Through the eventual conflict between Hiram and his grandfather, the reader sees the main theme. Not all cultural constructs are good. Some are hateful and evil, but those are also perpetuated by people teaching their kids to be hateful. In Mississippi, that has led to the perpetual racism that shapes the story of Emmett Till's death. Hiram hates that his grandfather was involved, but that helps explain his own troubled relationship with his father, because his father faced that hatred and resisted it.
The equality of humankind
The novel focuses on Hiram's belief that all people are valuable. He is friends with racists without knowing it, but he also friends with Emmett Till. Whereas his grandfather helped to kill Till, Hiram saves him from drowning. He sees the value in human life, without respect to racist ideas about ethnicity. The equality of humankind is not well-respected in Hiram's community, because Till's murder happens without justice.
Identity and evil
The novel features an archetypal encounter with the evil patriarch of yesteryear. Hiram understands that his father is not perfect, but understanding his grandfather's racism opens up a whole new kind of awareness. He didn't know that his own family had the deep-seated racism that he hates in his community. Whereas evil seemed like other people's problems, he must admit that, since his own grandfather helped to lynch Till, that evil is not as far from home as he thought. He must decide for himself who he really is, and how he can treat the character issues in himself that he learns about in his family.
