After killing the king, Macbeth returns to Lady Macbeth, deeply shaken by what he has just done. He is in a state of emotional turmoil, overwhelmed with feelings of fear and guilt. His primary motivation is pity and concern for himself, as he expresses his fears and his feelings to Lady Macbeth. First he tells her that he could not respond when Duncan's attendants' murmured, "God bless us!":
But wherefore could not I pronounce "Amen"?
I had most need of blessing and "Amen"
Stuck in my throat.
For Macbeth to think of being blessed at this time shows his complete absorption with self, and it indicates his awareness of the mortal sin he has committed.
He then speaks of hearing a voice cry out:
Sleep no more!
Macbeth does murder sleep--
When Lady Macbeth questions what he had heard, he continues in more detail:
Still it cried "Sleep no more!" to all the house:
"Glamis hath murdered sleep, and therefore Cawdor
Shall sleep no more: Macbeth shall sleep no more."
Had such voices actually cried out, the castle would surely be astir, but it is not. The voices are born of Macbeth's imagination reflecting his deep guilt over murdering Duncan and his realization of the reality of his actions. "Innocent sleep" will now be denied him; he will have no peace. He refuses to return to the murdered Duncan's chamber to return the daggers he has carried away from the scene:
I am afraid to think what I have done;
Look on 't again I dare not.
Macbeth's reactions following Duncan's murder show that he is motivated by terrible guilt and fear and that his pity extends only to himself.