Which term signifies the underlying message or insight presented by the author?

The correct term that signifies the underlying message or insight presented by the author is the theme. The theme goes beyond the surface-level details of a text and represents the deeper meaning or central concept that the author aims to convey. It encompasses the universal ideas or moral lessons that can be derived from the narrative or argument, allowing readers to explore the implications and resonances of the story or text.

The main idea refers to the primary point or argument presented in a piece, but it does not necessarily capture the more profound insights or messages embedded within the work. Supporting details are facts, examples, or descriptions that bolster the main idea but are not the overarching insights themselves. The topic is merely the subject matter being discussed and does not reflect the deeper messages or themes that may arise from that subject.