The witches are supernatural beings who appear at various points throughout the play. Their role is to prophesy events that will happen later on in the story. For example, they tell Macbeth that he will be king if he kills Duncan. Later on, this prediction comes true. The witches also have the power to manipulate people into doing their bidding. For instance, they convince Banquo to follow them into the woods, which ultimately leads to his death. Overall, the witches serve as a metaphor for fate or destiny, suggesting that our lives are predetermined by outside forces beyond our control.