Final answer:
The witches in Macbeth tell the story about killing a sailor's wife to show the dangers of wicked wives and to establish their evil nature.
Step-by-step explanation:
The witches in Macbeth tell a story about killing a sailor because of his wife to show that wicked wives can ruin the lives of their husbands. This serves as a cautionary tale about the dangers of trusting and being influenced by one's spouse. It also highlights the evil nature of the witches and further establishes their role as antagonists in the play.