The theme is "the central idea that the writing explores" (Glatch, 2024). Let's think of it as a fairly general notion. Here are a few examples:
Circle of life
Coming of age
Forbidden love
Man vs. nature
Redemption
Revenge
The American Dream
War
During or after you've written a story, you can easily identify the theme contained therein.
The message is "a specific idea that the author is trying to convey to the reader". Some writers go to great lengths to send a message through their stories, and you can do likewise if it helps you write better.
However, other writers strongly object to messages. Ursula K. Le Guin wrote, "The notion that a story has a message assumes that it can be reduced to a few abstract words, neatly summarized in a school or college examination paper or a brisk critical review." Indeed, if your story can be replaced by a single sentence summarizing everything of value in it, why did you bother to write the whole thing? Mark Twain wrote, "Persons attempting to find a motive in this narrative will be prosecuted; persons attempting to find a moral in it will be banished; persons attempting to find a plot in it will be shot."
Many people hold the view that messages are for readers to discover. If you ask the reader, they'll tell you what they learned or felt.
Egan, J. (n.d.). ENG134 – Literary Genres. The American Women's College. Retrieved 2024.
Glatch, S. (2024). What is Theme? A Look at 20 Common Themes in Literature. Writers.com.
Le Guin, U. K. (2005). A Message About Messages. CBC Magazine.
Twain, M. (1885). Adventures of Huckleberry Finn.