The major theme of the story is whether or not the story is fueled by the free will of Macbeth, or by his fate. The witches play the role of fate in the story. There are three of them, which represent the three fates. They advance the story because they show Macbeth his own fate. Knowing his fate, in his opinion, he has to act on every decision because he has no choice. “From this moment / The very firstlings of my heart shall be / The firstlings of my hand.” He vows in the future to act on every impulse, and decides to attack Macduff's castle and kill anyone connected to him. The witches are the biggest influences on Macbeth’s ‘decisions’ because of the fate that they have shown him.