She asks the spirits to make her blood thick, which means that she wants to become evil so that she can kill the king and not feel guilty about it. She calls upon the spirits and requests, "Make thick my blood. Stop up th' access and passage to remorse," (1.5.50-51). The blood represents the evil that she wants to consume in order to commit the murder.
Once Duncan is murdered, the meaning of blood transitions to guilt. After the murder, Macbeth brings the bloody daggers back; however, he was supposed to leave them in Duncan's chamber. He cannot think clearly now that the murder has happened. Lady Macbeth questions, "Why did you bring these daggers from the place? They must lie there. Go, carry them and smear The sleepy grooms with blood," (2.2.62-64). The blood symbolizes the guilt with which they will frame the guards. Macbeth cannot wash the blood off of his hands, meaning he cannot rid himself of the guilt and will always have the image of murdering King Duncan in his conscience. Macbeth expresses, "Will all great Neptune's ocean wash this blood Clean from my hand? No, this my hand will rather The multitudinous seas in incarnadine," (2.2.78-80). The blood on his hands represents the guilt that will not leave him; all of the blood will turn the ocean red, meaning he will always contain this enormous amount of guilt. .
After the murders have been committed, the meaning of blood transitions even more to guilt. Lady Macbeth changes from being ready to kill anybody to being resentful and scared of what will happen to her in the future. It is revealed that she has become regretful when Lady Macbeth sleepwalks in the castle and thinks she sees blood everywhere. She tries to get the blood off of her hands but it will not come off. The doctor observes Lady Macbeth crying, "Yet who would have thought the old man to have had so much blood in him?" (5.1.41-42). This horrific image of blood symbolizes the guilt of which she will never rid herself.
