Orson Scott Card gets most things right. One of the many things he got right for me was the development of theme in a story.
Uncle Orson says that stories written to expound on a theme tend to be sermons, not stories. Stories rely on chains of causality. Theme arises during the process of writing the story.
That is how it works for me. When writing a story I concentrate on the characters, the action, the dialogue, and the setting. I generally know the direction in which the story is going and approximately where it will end.
Then, somehow in the characters' striving, a theme will arise.
I did not set out to make Suffrage about how bitterness about the past spiritually kills us and must be put aside in order to live.
I did not set out to make Nirvana Cat about how adoption of a strictly rational world view kills the spiritual world view.
I did not set out to make Killing Words about how we feel more a part of our community when it is threatened; and how defending our community can give us a stronger love for that community.
Once the theme arises, I rewrite, emphasizing the theme in action and symbols. C. S. Lewis once said something like this. If we concentrate too much on getting to heaven, then we won't make it. We have to look to heaven, but live here on earth, day to day. I think if we concentrate on theme we do not develop the strongest theme we can. To build our strongest themese we write a story, and find the theme.