How do you figure out the main idea of a passage

Explain how beginning the story with the dialogue between Rainsford and Whitney contributes to both the author’s characterization of Rainsford and the story’s mood. Cite evidence from the story in your response.

The early conservation between Rainsford and Whitney foreshadows the events to come. Rainsford will soon experience the position of the Jaguar as he is hunted by Zaroff on Ship-Trap island. The brief exchange highlights Rainsford's outlook on the sport of hunting. He expresses a lack of empathy for the plight of the hunted. Over the course of his experience, his disposition changes remarkably.