Blood imagery serves two purposes in Shakespeare's tragedy Macbeth. It distinguishes between those who have might and those who rule by right. The following essay will show how the two patterns of imagery develop in the play.
The foreboding qualities of blood are first alluded to in Act 1 when King Duncan asks of the messenger, "what bloody man is this?" The implie oath in the archaic use of the word "bloody" points to the unhallowed associations of blood with those who would seize power from rightful authorities. Little does Duncan know he will soon be acquainted with the bloody mindedness of another of his kinsmen. The Thane of Cawdor has already betrayed his allegiance to the king in fighting on the side of the King of Norway. He was a man in whom Duncan placed "the utmost confidence." And yet, Scottish blood was shed defending the kingdom from him.
In Act II, all the "bloody business" is afoot as Lady Macbeth and Macbeth plot Duncan's murder. They will stab Duncan, and smear the faces of his sleeping guards with blood. Macbeth returns from the king's chambers with bloody hands, wrongfully bloodied in the murder of his king, his kinsman and his guest. He is so horrified by what he has done that he cannot return to the chamber to leave the bloody daggers. Lady Macbeth does the job for him, thinking it a minor task that stands in the way of their triumph. She thinks "a little water clears us of this deed." How wrong she is.
In Act 111, Banquo's murder provides the bloody backdrop for Macbeth's growing insanity. When Macbeth thinks he sees him at the banquet, he tells him "Never shake thy gory locks at me!" Of course there is no ghost. It is Macbeth's guilty conscience that afflicts him. Macbeth's imagination is now full of blood, and he plans further murders. .
Of course, rightful bloodlines must find their way back to the throne, and in Act V, Malcolm returns to Scotland with English and Irish reinforcements.