Most scholars agree that one of the most effective ways in which Shakespeare's writing communicates is through the combination (or clusters) of images: In this play, images of strength and weakness, as well as ability and inability, are played off one another constantly. A good example is the image of the "milk of human kindness" which resurfaces later in Lady Macbeth's assertion that she would have murdered her own child while breast-feeding it — a contrast to Macbeth's weakness. The color of milk, white, is also used by both Macbeth and his wife, as an image of cowardice, while red — the color of blood — represents not only courage and the energy of life but also terror and the curtailment of life.
Another image contrast that is used repeatedly throughout the play is that of sleep and sleeplessness. Not only is Duncan murdered while he sleeps, but also Macbeth, Banquo, and Lady Macbeth have their rest disturbed by dreams. When Macbeth remarks "Duncan is in his grave; after life's fitful fever he sleeps well" (Act III, Scene 2), he is recalling the words with which his conscience (or Fate) spoke to him immediately after the murder: "Glamis hath murder'd sleep, and therefore Cawdor / Shall sleep no more, Macbeth shall sleep no more!" (II:2,41–42)
