on Jane Friedman site:

I write novels for children and young adults, and one of the hazards of my profession is the temptation to craft stories as expressions of something we want to teach to young people. In other words, having a “message,” a “point to make,” or wanting to impose a “moral” as the core of the novel. Don’t be a bully. Think for yourself. Share your (metaphorical) toys.

I’m not saying there’s anything wrong with those sentiments—far from it. But in my opinion, the best novels—for kids and for adults—are much more than the thin chocolate coating around the nut of a central “message.” They are richer, deeper, and more organically crafted than that.

On the other hand, some novels don’t seem to have any larger themes to impart, at all. Or they attempt to impart a larger meaning, but it comes out muddled.

At both ends of the spectrum, the authors have failed to find their novel’s true and vital theme.

Granted, this can be tricky. But over the years, I’ve found a way to mine deep below the surface of the novel I’m writing and discover its proper theme. More often than not, I find that the theme is in there already; I’ve put it in subconsciously. Now all that remains is to bring it to the surface and buff it to a high gloss. I’ll show you how this works for me, in four steps.