An author e-mailed me this week to say someone else had turned down their ms. saying it didn't have a theme. She said themes were what she wrote in grade school, so what did the editor mean by that??? How could a novel be a theme?
In writing, the term "theme" means what the piece is about. Simple and most of us know it, but I didn't know it when I started, and some may not know it yet.
Every novel, yes, every piece of writng has a theme and The Theme of any work is usually a grain of universal truth that can be said in one line.
The action in a story is then used to illustrate the theme. Right now one of the hottest shows on TV is TRUE BLOOD, based on the Sookie Stackhouse books by Charlaine Harris. The theme of those books (yes, all of them!) is that it's okay to be different.
Sookie is different, because she's a telepath. Bill and Eric are different, because they're vampires. But basically they are okay, the good guys, and doing their personal best to fight evil as they see it, regardless of what others may think of them.
Nobody can tell your personal truth but you. You will find as you write more and more that the same themes, often related to your deepest beliefs, will surface again and again in your work.