"What, can the devil speak true?” The meaning of the quote is (translation): What, can the devil say the truth?. After Macbeth is made Thane of cowdor, Banquo is starting to believe the these prophecies. He find the fact that the prophecy came true bizarre. Witches were considered evil however he believes that their powers actually work. He is accepting that they are not always associated with evil because Macbeth became Thane of cowdor which is a positive thing.