Except they meant to bathe in reeking wounds,
Or memorize another Golgotha,
I cannot tell—
But I am faint, my gashes cry for help. (1.2.39–42)

A wounded captain fresh from the battlefield reports to King Duncan on Macbeth and Banquo’s bloody actions on the battlefield. The captain says Macbeth and Banquo’s behaviors were so ferocious and bloodthirsty, it was as if they were trying to make the battlefield as infamous as Christ’s crucifixion at Golgotha. The bloodiness of the battle symbolizes the brutality of the war and a latent ruthlessness in Macbeth’s nature.

Will all great Neptune’s ocean wash this blood
Clean from my hand? (2.2.60–62)

After he kills Duncan, Macbeth comes to Lady Macbeth with his hands covered in blood. Horrified by his act, Macbeth laments that not even all of “Neptune’s ocean” would be enough to clean his hands. The blood on Macbeth’s hands symbolizes the guilt he feels for murdering Duncan.

Out, damned spot! Out, I say! . . . who would have thought the old man to have had so much blood in him. (5.1.25–28)

Lady Macbeth speaks these words at the end of the play, wandering around the castle in a delirium trying to wash out an invisible bloodstain, a symbol of her guilt. In the beginning of the play, Lady Macbeth appears more ruthless than her husband, but by the end of the play, she finally succumbs to the looming guilt for her crimes, and she is unable to cope with the reality of what she’s done.

I see thee still,
And on thy blade and dudgeon gouts of blood,
Which was not so before. There’s no such thing.
It is the bloody business which informs
Thus to mine eyes. (2.1.45–49)

Just before he murders Duncan, Macbeth sees a vision of a dagger floating in front of him in the castle. The tip of the dagger points toward Duncan, and the handle points toward Macbeth. For a moment, Macbeth wonders whether the dagger is real. Here, when he sees that there is blood on the tip, Macbeth concludes that the dagger is not real but a manifestation of his guilt for plotting against Duncan. The blood on the dagger symbolizes Duncan’s impending murder and the guilt that will plague Macbeth for the rest of the play.

I am in blood
Stepped in so far that, should I wade no more,
Returning were as tedious as go o’er. (3.4.142–144)

After Lady Macbeth excuses the guests from the banquet hall, she turns to Macbeth to answer for his crazed outbursts. Shaken from seeing the ghost of Banquo, Macbeth now believes he is no longer safe, even from the dead, and is committed to doing whatever he needs to do to secure his safety. With the words “I am in blood / Stepped in so far” Macbeth reveals to his wife that he has already killed so many people that it will be too difficult to go back to being good. Here, blood symbolizes both Macbeth’s guilt and his newfound resolve to preserve his own life.