Shakespeare's tragedy of Macbeth is clearly built upon the workings of the imagination. For, Lady Macbeth's and Macbeth's fears, paranoia, and guilt emanate from the inner workings of their minds.
In Act III, Scene 4, Macbeth's envisioning of the apparition of Banquo represents the lack of spiritual comfort derived from this tragedy as Macbeth's conscience is always terrifyingly alive. When Macbeth moves to sit at the banquet table, he observes that all the seats have been taken; however, Lennox tells him there is a place for him. Hearing this, Macbeth suspects the lords of finding Banquo and bringing his body to the banquet in order to confront Macbeth with his murderous act. He asks, "Which of you have done this?" Then, he becomes defensive,
Thou canst not say I did it: never shake
Thy gory locks at me. (3.4.62-63)
In reality, Macbeth's guilt has originated from his horror of having slain Duncan, who was his friend. For, he perceives clearly the evil of the course he has taken as expressed in Act II.
To know my deed, ’twere best not know myself. Knock
Wake Duncan with thy knocking! I would thou couldst! (2.2.92-93)
Now in Act III, Macbeth is yet reeling from the turmoil in his conscience as he is not intrinsically an evil man; rather, he is one who, as evidenced from the testimony of the captain in Act I, is a man with the potential to be worthy.