Two truths are told
As happy prologues to the swelling act
Of th’imperial theme (1.3)
Macbeth speaks these lines as he realizes that the witches’ prophecy (that he will be Thane of Cawdor) has come true. He immediately starts to wonder whether this means that their third prophecy (that he will become king) will also be true. The eagerness with which he turns to this idea suggests that he finds the possibility appealing, even though he also realizes he would have to commit a terrible and violent act in order to achieve the position. These lines hint at Macbeth’s ambition and foreshadow his later actions even though, at this point in the play, he seems to refuse to consider acting upon it.
Thou wouldst be great
Art not without ambition, but without
The illness should attend it (1.5)
Lady Macbeth speaks these lines as she reflects on her husband’s character. She knows that Macbeth is capable of ambitious dreams, but she thinks that he is unwilling to display the ruthless behavior necessary to achieve those dreams. These lines reflect Lady Macbeth’s own philosophy of power, in which only individuals who are willing to set their morality aside will rise to greatness. They also show that she is a sound judge of character, and understands her husband very well.
I have no spur
To prick the sides of my intent, but only
Vaulting ambition, which o’erleaps itself
And falls on th’other (1.7)
Macbeth speaks these lines as he starts to doubt his plan to murder Duncan. He uses a complicated metaphor that compares his experience to horse-riding. He describes being unable to motivate himself to take action by likening himself to a rider who cannot use his spurs to motivate his horse to go faster. The one thing he does have is ambition, which he compares to a horse and rider who overestimate their ability to leap over an obstacle, and end up falling down. The passage describes the tension between Macbeth’s unwillingness to move ahead with his plan, and his acknowledgement that his ambition is leading him down a dangerous path.
To be thus is nothing, but to be safely thus (3.1)
Macbeth speaks this line after he has become king, but continues to feel restless and insecure. He is afraid that he might lose his position and is also frustrated by the fact that he has no heir. Without the knowledge that his lineage will continue after him, Macbeth finds it meaningless to be king. This quote reveals how him giving in to his ambition and murdering Duncan has not brought him peace, but rather has just left him more paranoid and anxious. The line also reveals how Macbeth’s first violent action sets off a chain reaction of him continuing to commit violent actions in order to maintain his hold on the power he has gained.