How does the motif of blood help set the tone in Macbeth?
Words like "blood," "bloody," and "bleed" occur some 50 times in the text of Shakespeare's Macbeth. Early in the play, Macbeth is viewed as valorous in battle because of the "bloody execution" that his sword brings about upon Duncan's enemies.
Macbeth's shedding of blood in Duncan's cause eventually leads to Macbeth engaging in "bloody business" in own cause against Duncan. Although Macbeth sheds the king's blood, he cannot bring himself, as Lady Macbeth instructs him, to "Smear / The sleepy grooms with blood," so she herself undertakes this mission.
One bloody deed begets another as Macbeth arranges to have Banquo killed. Macbeth rejoices to see Banquo's blood on the face of the assassin. All this shedding of blood, though, begins to weigh on Macbeth's mind and he becomes deeply disturbed after seeing Banquo's ghost: "It will have blood; they say, blood will have blood."
Not only will bloodshed drive Macbeth to distress, but likewise Lady Macbeth will also be tormented by her participation in these deeds. Eventually, she will imagine "the smell of the blood still" upon her skin, long after Duncan's death.
Not only do we see Macbeth shed blood, we also find the witches using blood as one of the key ingredients in their potions that allow them to prophesy the future to Macbeth.
Eventually, though, all of Macbeth's shedding of blood will bring him down once Macduff, Malcolm, and others discover what his crimes. They cannot stand by and allow their nation to be ruled by "an untitled tyrant bloody-scepter'd."
In the end, Macbeth is defeated by Macduff, who brings the horrific cycle of bloodshed to an end.
Thus, the frequent repetition of words like "blood," "bloody," and "bleeding" constantly keep before the mind's eye of the audience images of murder. There can be no doubt that this is a tragedy they see upon the stage.