The theme of a story is the underlying message or insight about life and human nature that the author explores through the narrative. It often reflects universal truths and can be interpreted in various ways by readers. The central idea, on the other hand, is the main point or primary focus of the story, summarizing what the story is primarily about.
In essence, the theme is more abstract and monumental, often applying beyond the specific story, while the central idea is more concrete, describing the specific events and actions that take place within that story.