Twain takes advantage of the conversation between Huck and Joanna to deliver a number of comments about the concept of royalty and the idea that some people are better than others due to birth to a particular family. His argument with the distinctions didn't stop with the monarchy - Twain points out the ridiculous nature of having servants as well as monarchs.
I forgot I was the old man's servant. But next minute I whirled in on a kind of an explanation how a valley was different from a common servant, and had to go to church whether he wanted to or not, and set with the family, on account of it's being the law.
This chapter also addresses, once again, the struggles Huck has with his conscience as he observes the duke and the king preparing to carry out their plan to rob the girls of the inheritance money. As he comes to recognize the true good and loving nature of the sisters, he realizes that he can't allow the scoundrels to take the money, regardless of the trouble he would have if they found out about his involvement in ruining their plot.