It creates a sense of futility in the entire adventure that Jim Huck and Tom have went on. It also helps to explain why Tom didn't feel bad about helping Jim escape despite the fact that he doesn't believe that slaves are free people. It creates a sense of irony that the entire story was about helping Jim escape a fate that he had already escaped. Last but not least it created moral ambiguity about Miss Watson. Early in you could think of her as a mean person, but suddenly you realize that she wasn't a bad person and that she had the capacity to be kind to slaves.