Macbeth uses this metaphor to compare his ambition to a horse rider who falls when he jumps higher than he is able. In these lines Macbeth recognizes that he has no other reason to kill Duncan than his own ambition. This blatant recognition of his dangerous ambition makes Macbeth's eventual murder of Duncan ironic.

Having been persuaded by Lady Macbeth, Macbeth finally agrees to carry out the plan to murder Duncan. He tells her to go and entertain the guests ("mock the time with fairest show") and hide her true intentions as if everything is as it should be.

Lady Macbeth tells her husband to shore up his courage and hold it to him by using a metaphor that refers to the notch on a cross-bow that holds the taut string before firing. Lady Macbeth's metaphor is ironic because it draws a connection between Macbeth's act of selfish ambition and a soldier stringing a bow. Soldiers act on behalf of the king and country, while Macbeth acts on his own accord. In this way, Lady Macbeth not only tells him to "tighten" his courage so that they don't fail, she metaphorically elevates the purpose for his courage and justifies their actions.

Lady Macbeth's reply to Macbeth has many interpretations: It could be a scornful reproach, or if the accent is on “we,” the response can be viewed as a contemptuous exclamation. Another interpretation is a response to his question, suggesting that if they fail, that will be the end of them. This last response portrays Lady Macbeth in a more characteristic light as a person of strong determination who can coolly consider the possibility of failure. Note how she doesn’t dwell on this, and immediately assures him of their success.

These lines heavily suggest that Macbeth initially had the idea of killing Duncan to become king and shared that plan with his wife. She tells him that when he dared (durst) to make the plan at the time, he was truly a man then.

Lady Macbeth responds to her husband by asking what could have possibly made him break his promise to her. In this context, enterprise refers to the bold, arduous, or momentous undertaking they have been planning: the murder of Duncan and Macbeth's ascension to the throne.

Macbeth's reaction shows how much he resents being called a coward. He states that he does all of the necessary things that make him a man—which we can read as an honorable man. He considers those who do more than these things, such as wicked or evil actions, as dishonorable, or unmanly, men. Macbeth's defense gives us some insight into the values that he has regarding proper behavior and why he does not want to carry out the plan.

"Prithee" is an archaic interjection which is used to express a wish or request. ("I pray thee," or "I beg of you.") In this instance, when Macbeth requests "peace," he is expressing a desire for his wife to stop discussing this matter altogether.

Lady Macbeth states that Macbeth's love for her is no stronger than his lack of ambition for the throne, and then she proceeds to accuse him of cowardice—a very strong insult to make against a soldier. Notice how she targets all of her taunts as specific points to make Macbeth reveal what he truly fears about killing Duncan and how she convinces him to come around to her way of thinking.

In another clothing metaphor that extends from and builds on Macbeth's previous comments, Lady Macbeth accuses him of a lack of resolution to carry out the plan. Here, "hope" initially refers to Macbeth as a person drunk with the idea of success, and then becomes the robe that Macbeth has dressed himself in that has become pale and weak.

This brief exchange reveals how much Macbeth loves Duncan: he cannot sit in the same room with the man he is planning to murder. Lady Macbeth's reply indicates that Duncan obviously loves Macbeth because he has always been an honest and honorable man. Macbeth is in an unfamiliar role that he is uncomfortable playing. Shakespeare uses moments like this to maintain a degree of sympathy for Macbeth, since the tragedy of the play is his downfall.

In Shakespeare's day, a "trammel" meant a net with three layers used for catching birds or fish. Macbeth uses this expression to voice his doubt that assassinating Duncan can be done in a way that will "net up" all the consequences of that action and "catch" success.

Macbeth admits that Duncan has been a worthy king, which adds to the difficulties Macbeth has with plotting Duncan's murder: Duncan has not been a tyrant whose death will bring relief to the land, and because he is so honorable, his death will bring grief to the land.

According to the Oxford English Dictionary, Shakespeare coined this phrase and all other uses since then are borrowed from him. Generally, be-all means something which is or constitutes the whole, and the end-all refers to something that ends all or finishes something. Macbeth wishes that this blow, killing Duncan, could be self-contained and without consequences.

Macbeth is saying two things. One is that he would like to get the murder over and done with because the ideas connected to it are driving him crazy. He also references the fact that he may never again have as good an opportunity to do it, since King Duncan is an overnight guest, and he is at Macbeth's mercy.

What Macbeth means is that if a man dares to do dishonorable things he is not a real man. It is "unmanly" to do wicked deeds. While Macbeth is using "man" to mean more generally a "man of honor," he is also creating a dichotomy between himself and his wife, who is not a man in either of the two senses and acts independently of honor and morals.

Macbeth is using horseback riding as a metaphor when he says he has no spur to prick the sides of his intent. Where he says, "...but only Vaulting ambition," he evidently is thinking of the image of a man who intends to leap onto a horse but vaults so high that he goes clear over the horse's saddle and falls to the ground on the other side. The word "side" is left out because Macbeth's soliloquy is interrupted by his wife, but the audience should understand the missing word because of all that went before it, beginning with "I have no spur." A man who did such a thing would look foolish, and Macbeth is apparently thinking that it is foolhardy to be plotting an assassination when he has no real need of further advancement and no just reason for wanting to replace the existing monarch. The alternative to being foolish is to be wise, and Macbeth is thinking that his better wisdom is telling him to abort this whole assassination plot.

"Prithee, peace!" is a polite way of saying, "Stop—Enough, already!" Macbeth's wife has been driving him crazy by urging him to do something that goes against his character, his sense of duty, his sense of honor, and everything else in his nature. When he says, "Prithee, peace!" he does not just mean, "Please stop talking for now," but "Please stop talking about this matter altogether." But it doesn't do any good. She just takes another tack when she asks,

What beast was't then
That made you break this enterprise to me?

In effect, she is saying, "It wasn't my idea to kill the King. It was your idea."

Lady Macbeth is concerned that her husband has left the dining chamber and won't return, which looks suspicious and is also rude. Macbeth was likely finding it difficult to talk to Duncan in a cordial manner while he was secretly thinking about murdering him. Lady Macbeth can't understand this because for her such duplicity comes easily.

Macbeth’s foretelling the future consequences of assassinating King Duncan should be compared with Marc Antony's soliloquy in Julius Caesar, act III, scene I. In both, Shakespeare summarizes what actually happens by using the future tense rather than the past tense. Both Macbeth and Antony predict what will happen as consequences of wicked violence. This is a shorthand way for Shakespeare to cover years of chaotic historical events in single speeches rather than attempting to dramatize or describe them onstage.

There has long been speculation about the childless marriage of Lady Macbeth and Macbeth. These lines show that Lady Macbeth has had a baby at least once (her phrase "given suck" is a reference to nursing), but whether that child was from a previous marriage or has died is left unknown.

Audiences in Shakespeare's time (and indeed to some contemporary audiences) would have been especially troubled by Lady Macbeth's "rule" over her husband, as early modern men were "enjoined" to keep their women under their control, supervising both women's actions and their speech. Macbeth's failure to "rule" his wife would have been viewed as "unnatural."

As stated earlier in the play, references to clothing are often metaphors for titles and ranks. Macbeth does not wish to go through with the plan to murder Duncan and take the title of king. He was only recently given the title of Thane of Cawdor, and wants to embrace it—and the accompanying respect—for a while.