Macbeth complains that dead men used to stay dead, but now they rise from the grave and annoy him.
When Macbeth and his guest gather for a banquet, he first stops to talk to the murderers to make sure Banquo and Fleance are dead. They tell him Banquo had his throat cut, but Fleance escaped. He is annoyed, but he goes back to his party. Unfortunately, he finds out the table’s full. The ghost of Banquo is sitting in his seat!
Macbeth panics. His guests and his wife do not see the ghost, so that don’t understand what he’s talking about. Lady Macbeth tells him he needs to cut it out, but he complains that dead men just aren’t staying dead anymore.
The time has been,
That, when the brains were out, the man would die,(95)
And there an end; but now they rise again… (Act III, Scene 3, p. 41)
As funny as this line is, it demonstrates that Macbeth is slowly losing it. He is becoming more and more out of touch with reality, and more and more paranoid. It is not guilt that forms the ghost, but fear. He sees Banquo as a threat, and is worried that he did not properly vanquish it by killing him.
In Act Three, Scene 4, Macbeth complains that the murdered men, particularly Banquo, have come back from the dead to haunt and terrify him. After briefly learning that the assassins were able to kill Banquo but not his son, Fleance, Macbeth comments that he is experiencing feelings of fear and uncertainty again. Macbeth then attends a feast with the nobles and begins to hallucinate. Macbeth is terrified when he sees the ghost of Banquo sitting at the table. Upon noticing Banquo's ghost, Macbeth begins speaking to the apparition which worries his wife. Macbeth then complains to his wife that the murdered men no longer stay dead in their graves and insist on haunting the living. He says,
"The time has been that, when the brains were out, the man would die, and there an end. But now they rise again with twenty mortal murders on their crowns and push us from our stools. This is more strange than such a murder is" (3.4.81-86).
Macbeth then gives a toast and Banquo's ghost returns once more. Macbeth commands the ghost to leave and stay in its grave. After Banquo's ghost exits, Macbeth explains to his guest that he is ill and the feast ends.