A couple of important things are laid out in this scene. First, this is the scene in which Macbeth kills Duncan. Secondly, the audience gets a clear picture that Macbeth actually does have a soul as witnessed by his guilty conscience, whereas Lady Macbeth seems to not. While he makes statements such as: "I'll go no more: I am afraid to think what I have done;
Look on't again I dare not," she is all practicality in the face of the horrible deed, telling him to: "Go get some water,
And wash this filthy witness from your hand.
Why did you bring these daggers from the place?
They must lie there: go carry them; and smear
The sleepy grooms with blood."
In Act II, Scene 2 of "Macbeth," Shakespeare takes two decisive and what appear to be strong characters and reduces them both to nervous and guilt-ridden murderers. Lady Macbeth also becomes the dominant figure in the relationship with her husband by taking charge of the murder weapon and becoming the practical one. She tries to reassure her husband and that the worst is over, that everything will be all right if he will only get over his nerves and stop thinking about the crime.
It is this scene that invokes the "blood on the hands" that will not wash off (not literally, but figuratively) which is the recurring horror for Lady Macbeth.