[Chapter 42] How does Tom's revealed knowledge of Miss Watson's will complete the theme of moral ambiguity?

When the boys find out that Miss Watson set Jim free in her will, they realize that even she felt a great deal of remorse for the action she almost carried out: namely, to sell Jim. This completes the moral ambiguity precisely because it's difficult to pinpoint one person who represents the "bad guy."

Throughout the novel, Huck has been struggling with his decision to steal a slave. He's been taught by society that this is a grave sin. On the other hand, his conscience says that he's doing right. When we find out that Jim was free all along, the "crime" is no longer a crime. Hence Huck will not be charged with stealing a slave. He once believed he would go to hell for not returning Jim to Miss Watson. Now, he won't . . . but he still chooses to leave society and go somewhere else where the law isn't so "cut and dried" and distasteful to him.