Answer:
The purpose of the witches' prophecy in Macbeth is to foreshadow the play's events and emphasize the theme of fate and free will. The prophecy sets the plot in motion and leads Macbeth to believe he is destined to become king, prompting him to take action to fulfill the prophecy. The witches' words also create a sense of ambiguity and uncertainty, leaving the audience to wonder if the events of the play are predetermined or if the characters have control over their own fate.