In these early chapters, Twain is satirizing the "sivilized" sciety that Huck has found himself thrust into. Most notably, the characters of the Widow Douglas and Miss Watson prove themselves religious and moral hypocrites. One of the more minor acts of hypocrisy Huck notices while in their care is the matter of smoking. He reports it thus:
Pretty soon I wanted to smoke, and asked the widow to let me. But she wouldn't. She said it was a mean practice and wasn't clean, and I must try to not do it any more. That is just the way with some people. They get down on a thing when they don't know nothing about it. Here she was a-bothering about Moses, which was no kin to her, and no use to anybody, being gone, you see, yet finding a power of fault with me for doing a thing that had some good in it. And she took snuff, too; of course that was all right, because she done it herself.
So she won't let Huck smoke, but she herself will consume tobacco in another form: the very definition of hypocrisy. This is just one example of the social criticism Twain offers. The most glaring examples come in the form of the two women's religious practices, and the fact that they own slaves. For Twain, and hopefully for all people who consider themselves moral or people of faith, this is one glaring contradiction that cannot be reconciled. Calling their slaves in to say prayers before nighttime shows that they themselves see no problem with this arrangement.
Although Huck can't name it yet, he knows that there is something very wrong with his situation. He doesn't recognize the discrepancy between Miss Watson's criticism of him, & her insistence on describing herself as a good person, one going to heaven. This shows his innate awareness of people's actions, and sets up his later decision to remain with Jim wihtout turning him in.