What are the prophecies the witches gave?
When Macbeth and Banquo encounter the three witches in Act 1, Scene 3, they prophecy that Macbeth will become Thane of Cawdor and that he will later become king. (They hail him as Thane of Glamis and Thane of Cawdor, but he is already Thane of Glamis). Then Banquo asks them to prophecy his own future, and they say that he will be father to a whole line of kings although he will never be king himself. Macbeth soon learns in the same scene that the current Thane of Cawdor is facing execution for treason and that King Duncan has appointed Macbeth Thane of Cawdor in his place. This makes a strong impression on him. Much later in Act 4, Scene 1, Macbeth encounters the witches again and receives further advice, not from the witches themselves but from a series of Apparitions.