The play Macbeth is highly concerned with the theme of free will and fate. From the beginning of this play, the three witches seem to indicate that Macbeth's fate is already determined for him. The idea of one's predetermined destiny is presented when the witches greet Macbeth.
All hail Macbeth, hail to thee, Thane of Glamis
All hail Macbeth, hail to thee, Thane of Cawdor
All hail Macbeth, thalt shall be king thereafter. (Act 1, scene 3, 46–48)
At first, Macbeth is confused to hear this. He is already Thane of Glamis but not of Cawdor, and he certainly does not expect to be king. However, shortly after, Duncan bestows the title of Thane of Cawdor on Macbeth. This gets Macbeth to thinking that he is indeed fated to be king.
Where the question of free will or fate comes in is that Macbeth has a choice to make. He never imagined that he would rule Scotland. "To become king / stands not within prospect of belief" (act 1, scene 3, 74–75).
Macbeth understands that there are few perceivable ways that he could become king. He would like it if fate granted him the position without him having to seize it himself. "If chance will have me king, why chance may crown me / Without my stir" (act 1, scene 3, 142–143). However, when Duncan announces that Malcolm will be his heir, Macbeth realizes that he will need to take his fate into his own hands.
Although it may appear that Macbeth's fate has been decided, Shakespeare shows the audience that Macbeth retains control over his free will. He nearly decides not to kill Duncan. He tells his conniving wife, "We will proceed no further in this business" (act 1, scene 7, 32). However, Lady Macbeth is eventually able to persuade her reluctant husband to do the deed. Macbeth is not driven by fate. It is his wife's persuasion that causes him to make his choice. As such, he exercises free will. When he takes the imaginary dagger in act 2, scene 1, he is symbolically exercising his will to take ownership of his destiny. He understands that he is responsible for his choices.