Final answer:
Macbeth envisions becoming king either by chance or by taking action, specifically considering the murder of King Duncan as a means to achieve his ambition.
Step-by-step explanation:
Macbeth imagines two different ways he could be crowned King. The first is through chance or fate, as he mentions in an aside, "If chance will have me king, why, chance may crown me, Without my stir." This indicates his initial belief that if he is destined to become king, it will happen without his intervention. However, Macbeth also contemplates action, particularly the possibility of murdering King Duncan to seize the throne. This is evident when he says, "The Prince of Cumberland! that is a step On which I must fall down, or else o'erleap," indicating that Duncan's son is an obstacle he must overcome, hinting at his eventual decision to commit regicide as the path to kingship.