How does Shakespeare characterize the witches in Macbeth?
Shakespeare characterizes the Weird Sisters as petty and vindictive creatures who enjoy manipulating others for their own amusement. In the first scene of the play, they say, "Fair is foul, and foul is fair," a paradox which implies that, in their coming interaction with Macbeth, they are going to make bad things seem good and good things seem bad (1.1.12). Therefore, when they deliver their prophecies to him, that he will become Thane of Cawdor and then king, it seems really good, and so we can assume that the prophecies are actually bad. Further, the first is not even a prophecy; Macbeth has already been named the Thane of Cawdor, he just doesn't know it yet. So, the sisters misrepresent this fact a bit. Banquo is concerned that the witches have attempted to gain their trust with "honest trifles" so that they can "betray" them "in deepest consequence." In other words, he's concerned that the witches told Macbeth one small truth in order to get him to believe the bigger prediction: that he will be king.
Prior to Macbeth and Banquo's arrival in scene 3, one witch describes how she is essentially going to torture a man as recompense for his wife's rudeness to her. She goes on to show her sisters a pilot's thumb which she just happens to have in her pocket. Therefore, we can understand that these witches are manipulative and mean, and they seek to deceive Macbeth in order to see what terrible things he will do in order to make the prophecy come true. Later, when they convene with Hecate in Act 3, scene 5, her statement that "security / Is mortals' chiefest enemy" confirms their deception and intention to destroy Macbeth by putting his own flaws to work for them.
In Macbeth, Shakespeare characterizes the witches as the harbingers of fate and destiny. In the first scene of the play, the witches meet and indirectly state the events that they foresee. By starting the play with a scene in which only the witches appear, Shakespeare is suggesting that the play will be a battle between one man's fate and free will. This is confirmed in Act 1 Scene 3 when Macbeth and Banquo meet the witches and Macbeth then thinks about how he will make his prophecy come true while Banquo remains wary and untrusting of the witches. Superstition causes viewers and readers to see the witches as evil; however, they words and actions revolve around "an eye for an eye," not evil (early in the play the witches talk about getting revenge on a man because his wife treated them poorly).