"Glamis hath murdered sleep, and therefore Cawdor shall sleep no more, Macbeth shall sleep no more". Does this have a reference to the evolution of the character of Macbeth? How do the stages reflect his transition? Why does Shakespeare choose to mention both titles. Why is the most innocent of the two titles chosen as the one that has murdered sleep? Since he became Cawdor he has murdered the king?
Here is the quote in question from Act 2, Scene 2:
Still it cried 'Sleep no more!' to all the house:
'Glamis hath murder'd sleep, and therefore Cawdor
Shall sleep no more; Macbeth shall sleep no more.'
There seems to be a strong probability that there was no voice crying out to all the house but that this was another of Macbeth's hallicinations, in this case an auditory hallucination. It seems to show that he is confused about his own identity. Is he Macbeth, or Glamis, or Cawdor? He would probably like to believe that at least a part of himself is innocent of the murder of King Duncan. Since he has so many different titles and identities, he can presumably blame the murder on only one of them while remaining innocent in at least one of his other identities. Shakespeare himself would like the viewer to regard Macbeth as partly innocent and not a total villain.
There is a certain logic in Macbeth's assumption because he has been torn between ambition and fealty, between guilt and innocence, between wanting the crown and wanting to be a true subject, friend, and kinsman of Duncan, between wanting his wife's love and wanting to go against her demands, since even before the beginning of the play.
The three identities named by the imaginary voice are not stages in the evolution of Macbeth's character; more likely, they are elements of his confusion about his real identity. Life used to be simpler for him when he was a good soldier and loyal subject of his feudal master. Once he began thinking about killing Duncan in order to become king himself, he became lost in a maze of identities and motivations. He is not a good villain. Being appointed thane of Cawdor came as a shock to him. It may have pleased his wife greatly, but it only added to his confusion. When Ross tells him:
And, for an earnest of a greater honour,
He bade me, from him, call thee thane of Cawdor:
In which addition, hail, most worthy thane!
For it is thine.
he reacts with suspicion:
The thane of Cawdor lives: why do you dress me
In borrow'd robes?
Here he is being addressed as the thane of Cawdor when the real thane of Cawdor is still alive. Macbeth subsequently experiences confusion about his identity throughout the play. He has to act innocent when he knows he is guilty. He has to play the king when he knows he doesn't deserve it, and when he realizes that none of his subordinates recognize him as the true king but only a pretender.
The voice he heard may have been telling him that he will be unable to sleep because he is too many different persons and can't get them all to go to sleep at the same time. If the guilty Glamis goes to sleep, the conscience-stricken Macbeth will lie awake regretting his treason, his treachery, his lying, his bloody murder of the man who loved him. There are two many people trying to sleep in the same bed. There is Glamis, Cawdor, Macbeth, and King Macbeth. And also, presumably, his equally guilty wife who is unsuccessfully trying to sleep beside him.
This seems to be what the imaginary voice was suggesting. When we ourselves experience insomina, it is as if there are at least two of us in the same bed. One would like very much to go to sleep and remain blissfully unconscious all night; but the other one is keeping us awake by counting the hours and thinking about past, present, and future, or just thinking a bunch of nonsense.