Nothing in his life
became him like the leaving of it.
Act 1, scene 4 is a continuation of the battle scene of Act 1, scene 2. Sandwiched in between is Macbeth's first encounter with the witches and their prophecy that he will be Thane of Cawdor. In scene 2, King Duncan has ordered Cawdor's execution, and here in scene 4, Malcolm, Duncan's son reports on how the execution went. For the Jacobeans who frequently witnessed executions by beheading, the prisoner pledging loyalty at the last minute was frequently rewarded with pardon. Cawdor, however, does not survive, in spite of confessing 'his treasons', imploring the King's 'pardon', and showing 'a deep repentance'.
...the milk of human kindness.
As Lady Macbeth waits for her husband to arrive home after she has received his letter with the news of his promotion and the prophecies, she decides that her husband will be king only through her iron determination since he is sometime too full of compassion, a very unmanly trait. The phrase is therefore at the top of Lady Macbeth's insult list so that when we use the phrase to approve of someone's compassion, we are changing it from an insult to a compliment.
The be-all and the end-all
According to the OED, Shakespeare invented this phrase and all subsequent uses by other authors are borrowed from the playwright. In the play, Macbeth is debating with himself about committing the murder of Duncan and becoming king without getting caught. If killing the King would have no consequences, he would have no other problems. But Macbeth knows regicide can never be so simple. For us, it means an event or person that is the beginning and end of all things in one package; an ego maniac; a conceited person.
Knock, knock. Who's there…?
In one of the very few comedy bits in Macbeth, the Porter is roused to open the gate just after the murder of Duncan. As he goes to the gate half asleep, he engages in a conversation with himself and several others of his own creation. It seems that Shakespeare is responsible for the beginning of the 'Knock Knock' joke. Variety, an entertainment industry magazine, reported on 19 August 1936 that America was caught up in a 'knock-knock craze', and on 14 November 1936, England fell for the tasteless pun answers to the question 'knock-knock' when radio comedian Wee Georgie Wood told several of the jokes on a radio show. Nowadays, the 'knock-knock' joke is an integral part of panto (short for pantomime), a form of interactive theatre that stages children's fairy tales, especially at Christmas in Great Britain.
What's done is done.
Here a very calm Lady Macbeth chides her husband for still thinking about Duncan's murder. She tries to tell him that there is nothing that can be done about it: dead is dead. Interestingly this advice to her husband emerges in a negative sentence in her sleep-walking: 'What's done cannot be undone' (5.1.68). Her guilty conscience is even more forceful than the seemingly simple advice she gives Macbeth. Not only can nothing be done about Duncan's murder, but...
(The entire section is 1360 words.)