In act 3, scene 1, Macbeth delivers his soliloquy before speaking to the two murderers. When the soliloquy occurs, Macbeth is worried about Banquo. Remember, before Macbeth expresses his thoughts about Banquo, Banquo reveals what he’s thinking about. Banquo is focused on “the weird women.” If they’re prediction about Macbeth came true, perhaps their prophecy about him will be realized. Thus, future kings won’t be Macbeth heirs but the sons of Banquo. Banquo is allured by this prospect, but not in the murderous, conniving manner of Macbeth. It doesn’t appear as if Banquo is ready to kill his way to the throne.
In his soliloquy, Macbeth focuses on the witches’ prophecy as well. Macbeth did not take down Duncan so that he could serve as a king for a little bit and then surrender the crown to the heirs of Banquo.
Think about how Macbeth’s obsession with being king, and his paranoia over Banquo, relates to the descriptive words. Near the end of the soliloquy, Macbeth uses language that conveys a sense of emptiness. He bemoans his potential “fruitless crown.” He feels as if a “barren sceptre” is in his hand.
The terms tie into the literary devices. The powerlessness that Macbeth feels is reflected in the symbols of vacantness. Macbeth also uses metaphor to manifest his infatuation with keeping the kingship in his family. He likens the crown to an “eternal jewel.” Of course, the crown is not literally a precious gem that Macbeth wants to keep forever; it’s a comparison that reinforces the extraordinary value that Macbeth attaches to the crown and his intent to hold on to that crown for as long as he possibly can.