What is the importance of the witches? Are they trustworthy?

The witches in Macbeth are present in only four scenes in the play, but Macbeth's fascination with them motivates much of the play's action. When they meet with Banquo and Macbeth, they address Macbeth with three titles: thane of Glamis, thane of Cawdor, and king hereafter. Next, they predict that Banquo will father kings, though he will not be king himself. Refusing to answer questions, they vanish. Later in III.v, Hecat lectures the witches for talking to Macbeth without involving her. In IV.i, when Macbeth pays another visit to the witches, Hecat has briefly appeared to the witches, but leaves before Macbeth's arrival. Though the Riverside edition has her accompanied by three other witches, most editions do not. In this scene, the witches make a thick gruel in a cauldron, using animal and human body parts. Many of the animals are reptilian or associated with night. The human body parts come from people who were considered outsiders to the Christian world of the English Renaissance: Jews, Turks, Tartars. The witches refer to their activity as a "deed without a name" (IV.i.49). They sense that Macbeth is coming; one says she can tell "By the pricking of my thumbs, / Something wicked this way comes" (IV.i.44-45). This time, the witches submit to some of Macbeth's questions. They pour in sow's blood and a murderer's blood into the cauldron, and produce apparitions. When Macbeth has seen the apparitions (see Apparitions) and heard their messages, he demands to know about Banquo. The weird sisters then produce a show of eight kings followed by Banquo. As the witches produce this display, they say "Show his eyes, and grieve his heart" (IV.i. 110). When Macbeth grows enraged, they dance and depart with great cheer.

There is a frustrating duplicity about the witches' nature as there is about their prophecies and predictions to Macbeth. They are interpreted variously as custodians of evil, spinners of the future, and as something slightly more neutral, creatures with knowledge of the future but with limited powers.