Huck Finn Notice Help

[snowboardtogo]

Persons attempting to find a motive in this narrative will be prosecuted;
persons attempting to find a moral in it will be banished;
persons attempting to find a plot in it will be shot.

At the beginning of the novel Huck Finn we see the above notice by the author Mark Twain. In what tone of voice do you imagine Mark Twain was speaking these words? What does he mean by it and why did he write us this notice?

I am not looking for the actual answer, just maybe some hints to get me started.

Thanks ahead of time!

[Hairy Faery]

We did this book for my book club, and the idea that went around for that opening was that Huck Finn can be dissected and studied and worked at so much that is takes the meaning out of the book. Huck's life was generally quite simple. Yes, he had issues about his father and so on but on the whole he was a boy floating naked, down a river. One member of the book club was not enjoying the book until it was mentioned to slow it down, read the page as Huck might have told the story...calm, easy and slowly.
So, I imagine that Mark Twain would have said it with a bit of humor, or a tone that would imply pure leisurely reading.