The art of fiction, like the art of stage magicians, is one of directing the audience's attention to what you want them to see.

Some writers find that they don't know their themes until they've finished the first draft (I am one). They then rewrite with an eye toward balancing on that tightrope: not too contrived, not too rambling; does what I'm saying about the world below me actually add up to anything? Other writers pay attention to these things as they write the first draft. Either way, an awareness of the macro and micro levels of theme can provide one more tool for thinking about what you should write, and how.

In commercial fiction especially, everything in the story usually contributes directly to the plot The shorter the story, the truer this is

Fiction is about stuff that's screwed up.

Every paragraph should accomplish two goals: advance the story, and develop your characters as complex human beings.