Which I have heard recently rephrased as work, workers, world, words, and wisdom. That helps explain why theme can be such a bear. One reason why books that preach are often failures is that the author doesn't have as much to preach as he thinks. He thinks he's discovered some New and Important Insight in the human condition, solving some conundrum that the best and wisest have been breaking their hearts over for millennia; the odds are against them. Or he's propounding a theory he's learned from someone else. This ups the odds for its being a good idea, but then, he has to fathom all the depths and complexities of the idea as applied to real life. Old ideas are better because they've been put to the test more, but then, as Samuel Johnson warned, "what is known is rejected, because it is not sufficiently considered that men more frequently require to be reminded than informed," and many writers are unaware of the tests, and how -- say, for instance -- a commune has to handle the collective action problem somehow.
Plus, of course, there's the question of whether writing can teach something. I have heard writing praised as a way to get into the thoughts of people very different from you -- but there's always the option of rejecting it as unrealistic characterization. I once wrote a short-short making fun of something I read, where the writer glamorized the boy declaring the emperor has no clothes on. The point of the story was that this is wise only when the emperor actually has no clothes on. Some people who read it -- who, in my experience, were not prone to shouting that the emperor has no clothes on -- found it very funny indeed. Other readers said it had no point, or even that they didn't think it was finished. After this I went looking at how various satires were treated. Amazingly, the people who always thought the satire was funny, funny, funny were those whom you could tell on other evidence had always hated the thing satirized. Frequently they overlooked the way a satire removed the point of an activity and then jeered at it for having no point. . . .
The medievals' thoughts on literature was that it should please and instruct. I think it very important that it should please, because all bets are off when it comes to instructing.