This is from C. S. Lewis, On Three Ways of Writing for Children.
Let the pictures tell you their own moral. For the moral inherent in them will rise from whatever spiritual roots you have succeeded in striking during the whole course of your life. But if they don't show you any moral, don't put one in. For the moral you put in is likely to be a platitude, or even a falsehood, skimmed from the surface of your consciousness...The only moral that is of any value is that which arises inevitably from the whole cast of the author's mind.Where Lewis wrote morals that arose from spiritual roots from his whole life, Pullman sets about to write simplistic anticlerical platitudes skimmed from the surface of consciousness.
I read this and I realize that Mr. Pullman set about to be the 'anti-Lewis' in more ways than one.