In Act II, scene II, Macbeth returns to Lady Macbeth right after he has murdered Duncan. In killing Duncan, Macbeth has stepped over a moral line and knows he can't go back. Shakespeare presents him as filled with agitation, guilt and foreboding. Macbeth ponders his terrible deed and wonders if he will ever be able to sleep again. "Macbeth does murder sleep," he says. His nerves are terribly on edge, and we can imagine him filled with adrenaline, pacing, excited, jittery, and talking too fast. Lady Macbeth tries to calm him, urging him not to think about what he has done.
He reacts with guilt and nerves when he hears someone knocking. Why is it, he asks, that "every noise appalls me?" He looks at his bloody hands and wonders, "Will all great Neptune’s ocean wash this blood/Clean from my hand?" He realizes, however, that nothing can wash away the guilt. Rather than the sea washing off his blood, his blood would make the "green one [sea] red." Nothing can rid him of his guilt.
Some of Macbeth's most famous speeches take place in this scene in which Shakespeare captures the extreme psychological agitation of a first-time murderer through Macbeth's heightened language.