What is Macbeth talking about in this quote, how does this relate to the plot, what is the significance of this quote and who is this spoken to?
To know my deed, ’twere best not know myself.
Wake Duncan with thy knocking. I would thou couldst.
This line is spoken by Macbeth. It is the last line of Act II, Scene 2.
I believe that Macbeth is speaking the two parts of this quote to two different people. The first part is said to his wife, the second part is said to someone that we do not see -- the person who is knocking on a door.
In this quote, Macbeth is showing how he is not really all that happy with his decision to kill King Duncan. The first line is saying that he wishes he were asleep or unconscious so he would not have to deal with the knowledge that he has killed the king. The second line is saying that he wishes the knocking could wake Duncan.
By saying these things, he is showing that he feels guilty for what he has done. This guilt will continue to be seen in the rest of the play, though Macbeth never does give in to his conscience -- he just keeps doing bad things in pursuit of power.
This is Macbeth's famous pronouncement in the murder scene of Macbeth. This is just after Macbeth has returned from Duncan's room, killing him in his sleep.
The first line is a brilliant index to Macbeth's character and tragic predicament. His tragedy lies not just in his ambition to become the king and the unlawful and unethical means by which he tries to realize it, it also lies in his ethical thinking, his self-reflexivity, his ability to explore the depths of his own psyche and that is what he says over here. It is the tragedy of active imagination and knowledge. He would have been fine not to know himself and contemplate the deed, having done it. But he knows both the deed and a good deal about himself rather tragically.
The second line has him showing his evil fangs again in a twisting movement as it were. He refers to the knocking on the southern entry of Inverness and rather sardonically invokes Duncan. He should wake, if he can, with this knocking. Read in a different way, the line may as well refer to the pathos of his impossible wish to undo what he has just done.