At the beginning of the play, Macbeth and Banquo are close friends and comrades in arms. They have fought side by side in battle, and Macbeth respects and admires Banquo. However, after Macbeth murders Duncan and becomes king, he begins to feel guilty and paranoid about his crime. He is afraid that Banquo will discover his secret and expose him, so he becomes increasingly distant and suspicious of Banquo.
In this scene, Macbeth's paranoia reaches its peak. He has arranged to have Banquo and his son, Fleance, murdered, and he is eagerly awaiting news of their deaths. He is so consumed by his guilt and fear that he can barely function. When he sees the ghost of Banquo at the banquet, he is terrified and begins to rave. This scene shows how far Macbeth has fallen from the noble warrior he was at the beginning of the play. He is now a broken and guilt-ridden man, haunted by the consequences of his actions.