At A Newbie's Guide to publishing, JA Konrath has an interesting entry about themes, and particularly the theme of his Lt. Jacqueline "Jack" Daniels thriller series. He concludes that the theme of his novels is:

Try the best you can, because trying is all you can do. But if you try too hard, life isn't worth living at all.

Why did I pick this theme?

I didn't. It picked me. Anyone who regularly reads this blog can see how my quest to become published, and my attitude toward this career, are tied into this philosophy. It's what I struggle with, and what I aspire to.

This is a good point. Writers don't need to cast around for some profound message. When we write, inevitably, during the course of tens of thousands of words, we reveal our philosophies.

Looking back on the books and stories Mary and I have written about John the Eunuch, I can quickly discern recurring themes:

Justice cannot often be found in the laws, if at all. John has rarely, if ever turned a perpetrator over to the authorities.

Life inflicts wounds which cannot be healed. For John this is literally true. Our job is not to find a miracle but to go on knowing there will be no miracles.

Most people's lives are largely shaped by the simple necessity of finding a way to live. Our minor characters are always scrambling to make a living by hook or by crook.

Bleak and mechanistic as society might seem, there exists the possibility that there is more to the world than we yet understand. Many of our characters are motivated by relgiious beliefs of different sorts and in every book there are hints of the supernatural, something else underlying the world of our senses.

None of these themes were calculated or placed in the books consciously. They simply reflect who the authors are.