What do we call the lesson or message that the author wants the reader to learn from a story?

The term that best describes the lesson or message the author intends for the reader to learn from a story is "theme." The theme represents the underlying idea or central concept that resonates throughout the narrative. It encapsulates the broader observation about life, society, or human nature that the author seeks to convey through the characters, plot, and setting.

While "moral" can be closely related to the lessons learned from fables or parables, it is more specific and often refers to a clear and direct lesson about right and wrong. Themes can be more complex and nuanced, addressing various aspects of the human experience rather than just a singular moral takeaway.

The terms "objective" and "message" might relate to a broader understanding of the author's intent, but neither fully captures the essence of a lesson that is intricately woven into the story's fabric like the theme does. Thus, the best answer in this context is "theme."