Why doesn't Macbeth just wait for the predictions to come true?
After being named Thane of Cawdor, why didn't he just sit back and wait to become king? Surely if the witches' predictions were right, it would have just happened without him doing anything.
Macbeth lets the witches predictions weigh on him, and when he hears that Banquo will have a lineage of kings, he begins to worry. Later when King Duncan announces that his son will become king after Duncan, Macbeth feels that he will need to act in order to fulfill the prophecies. When he speaks to his wife, she goads him into committing the murder by saying he is a coward. She tells him that a real man would take what belongs to him. Macbeth feels that if he were to wait and let fate take control, he may very well lose the chance at king because of Duncan’s edict and because of the prophecies the witches put upon Banquo. Macbeth did not realize that the witches’ prophecies were based on what Macbeth would do in the future. Had he not heard the prophecies at all, he may not have become king, but he would have been loved and would have been happy.
It's tough to just ponder what would happen if Macbeth did nothing, because to do so would be to ruin the whole point of the play.
What the witches succeed in doing is planting seeds in MacBeth's mind that will grow into a wild, unchecked, rancourous jungle of thorns and briars. "Full of scorpions is [his] mind" and two of the larger themes of the play include psychology and what happens when "o'vaulting ambition o'er leaps itself." In effect, the witches DO give him the choice to act or not, and MacBeth, ever the warrior / soldier, chooses a proactive path of action. In effect, the witches' prophecies have become a "self-fulfilling prophecy" and MacBeth himself makes them and the mental torment that follows, come true.
On another tract, yes, MacBeth might have done nothing and merely stood aside while things simply played themselves out. We must not forget that Banquo was also in the witches' prophecies and that there is an added sense of urgency for MacBeth. If he sits back and does nothing, will Banquo get the crown?
Thanks for your help everyone!