The turning point of the novel occurs when Huck decides to write a letter to Miss Watson, telling her where Jim is. When he is finished, he rips up the letter and say, "OK, I'll go to hell." Huck, who has been bothered by the fact that he is helping Jim to escape, is now willing to help Jim even if it means going "to hell". The resolution is somewhat problematic. Tom Sawyer arrives at the Phelps and succeeds in convincing Huck to follow his romantic ideas about helping Jim to escape. After getting shot, Tom reveals that Miss Watson has already freed Jim and all the nonsense he and Huck went through in order to free Jim has been meaningless. Jim also reveals that Pap is death, so Huck's attempt to escape from Pap by travelling with Jim, has also been meaningless. Huck then decides to leave for "Injun Territory" because Aunt Sally wants to "civilize" him and he has had enough of that. So Huck leaves Jim to fend for himself and sets out for new adventures. Thus the themes of freedom and approaching Twain for this ending and others have said the ending brilliantly depicts what happened to America after the civil war. Huck,like the rest of America, thought the slave problem has ended and focused their attention on the West,forgetting about the problems of former slaves.
Huck learns that telling lies can be a good thing, but also a good thing. (He lied to the people looking for runaway slaves, to save Jim, but then the supposed king and duke lied for selfish and greedy reasons)
The Mississippi River is very significant in the novel. It symbolizes freedom, it is the route to freedom. But then, it is also life.
Racism- It is a bad thing. Mark Twain sort of mentions it. When Huck says, oh a black man was shot, or dead, i forget which, Aunt Sally goes, oh, good thing no one was shot or killed. So basically, she didn't consider the black man a person.
Some themes to consider are racism and the hypocrisy of "civilized" society.