The weird sisters meet with Hecate, the goddess of witches. She rebukes the sisters for meddling with Macbeth without first consulting her. But she says she'll help them when Macbeth comes to see them tomorrow. She says that they'll show him visions that will give him confidence and "draw him to his confusion" (3.5.29).
Many productions of Macbeth cut this scene. It introduces Hecate, and establishes that the witches truly are out to get Macbeth. Many productions of the play prefer to keep the witches' motivations more vague.