In this quote, Huck is saying that it is better to be honest than lie in this particular situation. He is thinking about telling Mary Jane the truth. This will remove the blame from him and make her feel better.
His motives differ in these chapters because when he is lying now it is to help others, not just himself.
Twain doesn't involve Jim much in these chapters because he is trying to show Huck’s change and how he has matured. Also, he is making other points against society, not just slavery.
This shows that Hines character is greedy and cares about money more than
anything else. Twain uses him to symbolize society.
Huck likes Mary Jane. He tells her to go away because he doesn't want her to end up in this mess. He also feels she might tell about his plan. This is significant because he is not thinking about himself, he is thinking about Mary Jane over him. We can see that he has changed for the better and has morals.
Huck's statement shows the theme of gullibility. This is because the townspeople believe the king and are gullible believing his word when everyone can tell who the liar is.
The doctor represents the truth and reason.
At the end of chapter 30 the duke and king are still villians. This is because they threatened Huck and fought. Along with that they got drunk and they had many prior shenanigans prior to chapter 30.