Final answer:
In Act IV of Macbeth, Macbeth learns that he should be wary of Macduff and that he cannot be defeated by anyone born of a woman. He also learns that his castle is seemingly invulnerable.
Step-by-step explanation:
In Act IV of Macbeth, the main character encounters the witches again. During this encounter, Macbeth learns that he should be wary of Macduff, as the witches show him a vision of a line of future kings, with Banquo leading them. Macbeth also learns that he cannot be defeated by anyone born of a woman, as the witches tell him, "none of woman born shall harm Macbeth." Finally, the witches inform Macbeth that he will not be defeated until Birnam Wood comes to Dunsinane, leading Macbeth to believe that his castle is invulnerable.
Learn more about Macbeth's encounter with the witches in Act IV