What purpose do the three witches serve at the beginning of Macbeth?

Fair is foul, and foul is fair: / Hover through the fog and filthy air.

The opening scene of Macbeth not only introduces the audience to the supernatural element that will be carried throughout the play, but it also establishes a theme of disorder through the presence of the witches, the stormy weather, and the bleak landscape. The witches (or weird sisters) probably would have been portrayed on the stage as grotesque and ugly creatures.

Audience members in Early Modern England viewed witchcraft differently than audiences do today. At that time, many people, including King James I, believed in the presence of witches and their ability to harm and destroy virtuous people.

The witches agree that they will meet Macbeth at a particular time and place, suggesting the importance of that encounter, which will occur in Act I, Scene 3.