In act 3, scene 5, Hecate tells the other witches to meet her the next morning "at the pit of Acheron." In Greek mythology the river Acheron was one of the rivers in the underworld, and was known as "the river of woe." Hecate says that in or near this place, Macbeth shall "come to know his destiny." The fact that Macbeth is to know more of his "destiny" in this place is in itself an indication of how much he has already abused his power as king. The implication is that he has abused his power so much that his destiny already lies in the underworld, or, as we might know it today, hell.
Hecate goes on to say that Macbeth shall in the future "spurn fate, scorn death, and bear / He hopes 'bove wisdom, grace and fear." In other words, Hecate says that Macbeth will be foolish enough to think that he is more powerful than death and fate and beyond the reproaches of "wisdom, grace and fear." He will become hubristic. Here then Shakespeare warns the audience that Macbeth's abuses of power will become even worse than they already are. He will abuse his power so much that he will think he is a kind of god, above the laws and limitations placed upon men.
Hecate's prophecies soon become true. Shortly after this scene, in act 4, scene 2, Macbeth hires murderers to kill Macduff's wife and young children. The murder of innocent children is perhaps Macbeth's greatest abuse of his power, and marks the point where Macbeth has completely lost sight of the normal rules and morals which men are subject to.