Identify the sentiment Macbeth expresses at the end of Act Two, scene two in Shakespeare's Macbeth—what does this reveal about Macbeth's...

At the end of Act Two, scene two, of Shakespeare's
Macbeth, Macbeth closes the scene (when he hears a knocking at the
castle gate) by saying:

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Wake Duncan with thy knocking! I would thou
couldst! (93)

Very simply,
Macbeth is saying, "Go ahead and wake Duncan with your knocking...I
wish you could." He wishes that Duncan was not dead. I think
Macbeth's first response is remorse. (Remember, this was not only
his King he killed; Duncan was also his friend and his cousin.) Throughout the scene,
once Macbeth returns to his bedroom with blood on his hands and the murder weapons in
his hands, he has exhibited the signs of a man who is unraveling (mentally)—caused by
the terrible crime he has committed. He obsesses at first that when the guards mumble
"Amen" in their sleep, he cannot call down a blessing on himself as
well.

Macbeth also seems to be hearing things—but I think
it's impossible to know for sure whether they are supernatural occurrences or auditory
illusions. He says...

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Methought I heard a voice cry “Sleep no
more!

Macbeth doth Murder sleep”...
 (46-47)

Then, when Lady
Macbeth notes that he has brought evidence of their conspiracy and crime back with him,
she orders him to take the daggers back and smear the drugged guards with blood to make
them look guilty. Macbeth refuses, outright:

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I'll go no more:

I
am afraid to think what I have done;

Look on't again I dare
not. (64-66)

This all just
emphasizes Macbeth's original uncertainty about killing Duncan in Act One, scene seven.
The last time he and his wife spoke, he had said that he wanted to wait before killing
the King: Macbeth explained the he was still enjoying all the rewards that the King had
showered him with for his part in the recent war. At that point, Lady Macbeth literally
harassed him into agreeing, calling him names and insulting his manhood, his bravery.
She knew exactly what she was doing—and he agreed to go ahead with the
plan.

Macbeth's distress at the end of this scene shows
that while he gave in to his wife's demands, his heart was not in it. I believe that
Shakespeare emphasizes this so that the audience can see just how far Macbeth is willing
to go to become and remain King, all because of his tragic flaw—his vaulting ambition.
We also recognize a certain frailty in face of his wife's displeasure, for at the start
of the play, they are deeply in love. (By the end, he is a tyrant, and she goes insane
reliving their murderous acts.)

By seeing Macbeth this way
in Act Two, scene two, we can gauge the change in the man as he arranges for the murders
of his friend Banquo and the Macduff family, and his willingness to kill Young Siward
(in the young man's first battle) at the end of the play. Macbeth has sold his soul to
the "enemy" (the devil) by killing the King. He believes killing will get easier with
time, and he seems to be correct. We are better able to see his absolute moral
deterioration by the play's end. The only thing left to him is his valor—his bravery. In
face of all else, he will not beg for his life, but dies in battle—the only honor left
to him.