Big Idea

I believe that one of the biggest themes in MacBeth is how we are defined by our future. This is a major theme because if the witches never told MacBeth that he would be king then Lady MacBeth wouldn't have set up the murder. Also, Lady MacBeth would still be sane and not wandering around at night, telling people things she shouldn't be. Also, she would have been able to survive the entire play. MacBeth may just be Thane of Cawdor and never aspired to be king.
Also, if the witches never told Banquo that his children would be kings then MacBeth wouldn't have become paranoid. He has started to believe that the witches were always right. If he didn't hear this he would have been confident in his line surviving past him as king, but now, because he knows that Banquo's children will rule, he starts to kill innocent people and blame the murder on their children. Also, he would have never gone back to the Weird Sister and heard about MacDuff killing him after the woods move to a hill.