What is Twain saying about Southern culture in The Adventures of Huckleberry Finn (namely chapter 22)?
The novel arguably makes its most direct social statements in Chapter 22 (not its largest or most important arguments, but its most direct). The two chapters dealing with Boggs and Sherburn are rare in that they do not include Huck in the action to any significant extent.
When Sherburn is approached and threatened by the town's mob, he gives a speech about certain false views that this crowd holds of itself. Sherburn derides their claims of virtue and bravery, saying that they are instead cowards who are only capable of acting in the dark of night, as a mob, and so cannot rightfully be considered as "men".
Colonel Sherburn’s speech to the would-be lynch mob is a harsh invective against mob action of any kind.
The contrast between Sherburn's stated view of the men who make up the mob and the mob's apparent views of itself constitute a commentary on a false chivalry of a falsely genteel South. Far from being the honorable inheritors of great traditions, these men are instead merely full of hot air, as it were; better in their minds than they are in reality.
One of the novel's themes relates to the idea that Southern culture has a tendency to be self-serving and self-justifying, glorifying itself based on a pride that is graphically symbolized in the character of Pap - a man who resents the success of others, who feels insulated from blame by virtue of his birth, and who does little or nothing to justify this pride.