Blood plays a very significant role. It is one of the play's major motifs, appearing throughout the play any number of times. One dramatic appearance of the blood motif occurs shortly before Macbeth enters Duncan's chambers to murder him. He sees a daggar floating in the air before him. As Macbeth watches, horrified, blood appears on the dagger. Macbeth's "fatal vision" can be interpreted to symbolize his guilt for the action he is about to take. It also serves to foreshadow the terrible fate that will befall King Duncan momentarily.
After Duncan's murder, as Macbeth's deep and genuine guilt sets in, he speaks figuratively of the blood on his hands. Employing literary hyperbole, Shakespeare has his hero explain that there is so much blood on Macbeth's hands that if he were to thrust one of them into the ocean, there would be enough blood to turn the ocean read. Through this figurative language, the depth of Macbeth's guilt is made clear.
Finally, Shakespeare returns to the "blood on my hands" motif in the play's conclusion when Lady Macbeth sleepwalks through the castle, reliving the murders of Duncan and Banquo. In her disturbed emotional state, she sees actual blood on her hands and attempts to "wash it away" by rubbing her hands continually. Again, hyperbole is employed. Lady Macbeth says there is so much blood that all the perfumes in Arabia could not take away the smell of blood on her hands.
In these three passages, Shakespeare employs blood to emphasize the guilt in his two characters. Macbeth feels guilt immediately; his wife, although cold and calculating at first, is eventually consumed by her own.
"Bloody Macbeth, well he deserves the name"--underscores Macbeth's nature by aligning blood with his name, and foreshadows that he will feed and sustain his identity with blood:
Come, seeling night,
Scarf up the tender eye of pitiful day;
And with thy bloody and invisible hand
Cancel and tear to pieces that great bond
Which keeps me pale!
Also, shows Mac's paranoia: "It will have blood they say, blood will have blood."
And by negation, note the absence of the word "Blood" from Malcolm's speech--he refers to blood only twice, and not in reference to any solution he plans to effect, but rather in his awareness of Macbeth's nature: "I grant him bloody" and in understanding of the effect of Macbeth's nature on the country: "I think our country sinks beneath the yoke / It weeps, it bleeds . . . ."