The blood imagery in Macbeth is significant for several reasons. For one thing, it signifies that the essence of the victims' life have left; and, as such it symbolizes the loss of true humanness in Macbeth and Lady Macbeth, who are responsible for the murders. For, in shedding the blood of the God-like Duncan and the good Banquo, Macbeth and Lady Macbeth become stained with the sin of their bloody deeds which disrupt the natural order.
As a consequence of their bloody deeds, in their guilt Macbeth sees ghosts and Lady Macbeth envisions spots on the stairs that will not wash away: "Out damned spot! Out, I say! (4.3.39) Macbeth also ponders upon his murderous deeds:
Will all great Neptune's oceans this blood
Clean from my hand? No, this my hand will rather
The multitudinous seas incarnadine,
Making the green red. (2.2.60-63)
He anticipates having to pay for his crimes as he reflects,
It will have blood, they say; blood will have blood:
Stones have been known to move, and trees to speak;
Augurs and understood relations have
By maggot pies and choughs and nooks brought forth
The secret'st man of blood. (3.4.122-125)
Prevalent throughout the play, blood imagery unites the murderous acts of Macbeth with his and his wife's sins and guilt as well as unifying the play with the repetition of this imagery. For instance, in the first secene of Act IV, Macbeth sees the image of a bloody child uniting the blood imagery with the child imagery as he is told
none of woman born
Shall harm Macbeth. (4.1.80)
Finally, with so much imagery of blood, the horror of Macbeth's heinous deeds leaves a lasting effect upon the audience as they realize the terrible evil of "vaulting ambition."