After his guests are gone, Macbeth is alone thinking about things, and he says "Blood will have blood." This means that the blood of the victim will seek out the blood of his killer and avenge the murder. It is kind of like "eye for an eye, tooth for a tooth." This idea of revenge was popular in Elizabethan tragedies known as Elizabethan Revenge plays. The Elizabethans borrowed this concept from Roman playwrights like Seneca. The characteristics of Elizabethan Revenge plays were:
- A secret murder is committed by an evil person. Usually the victim was well-loved or innocent.
- A ghost of the victim appears to inform a person of the evil deed. Usually the ghost appears to a younger person, like a son.
- The younger person vows to avenge the death. A complicated plot ensues, with lots of twists and turns.
- The characters often descend into madness - either from guilt or from anger and sadness.
- The murder is either avenged, or not. Lots of people die. Sometimes there is justice and the murderer dies, but the avenger also often dies.
Does this sound familiar? Oh yeah! Sounds like Hamlet, for one, but you can also see similar elements in Macbeth.
Macbeth fears that Duncan and Banquo's deaths will be avenged by their families, so he has just cause for concern.
These words spoken by Macbeth towards the close of the Banquet Scene primarily relate to Macbeth's fear of retaliation/retribution. A secret murderer can never go unpunished, and Macbeth shall have to receive bloody retribution.
What Macbeth means to say fits well into the Elizabethan view of bloodshed and revenge. Elizabethan audience used to enjoy scenes of murder, bloodshed, acts of horror and revenge. The plays of Kyd, Marlowe, Shakespeare and others made ample use of the sensationalism involved in such dramatisation of blood-soaked violence. The idea of 'holy revenge' entered into the plays of Kyd and others from the Senecan Revenge tradition. It was thought to be right and justified to spill the blood of a murderer, and that's what Macbeth was afraid of.
There was certainly a lot of revenge and blood spilling in Elizabethan time and also during the reign of James I so the violent actions in the play do reflect the practices of the time.
Shakespeare based his story on Holingshed's Cronicles and combined the reigns of two kings: King Duff and King Duncan. King Duff was supposedly killed by Dunwald who was angry because King executed some of his relatives. Here also we have a theme of revenge.