About that Huck Finn author's note

"Humor must not professedly teach; it must not professedly preach. But it must do both if it would live forever. By forever, I mean thirty years.... I have always preached. That is the reason that I have lasted thirty years. If the humor came of its own accord and uninvited, I have allowed it a place in my sermon, but I was not writing the sermon for the sake of the humor. I should have written the sermon just the same, whether any humor applied for admission or not." -Mark Twain