Imagery also helps the reader understand that chaos reigns. Along with the blood and water imagery are other dark images.
On the night of Duncan's murder, the stars are hidden in the sky. We also hear stories of unnatural behaviour in the animal kingdom: a falcoln was killed by a mousing owl and Duncan's horses were said to have eaten themselves. This image of the animals being out of control reflects the unnaturalness of the situation. Macbeth himself is like the mousing owl who killed the falcoln--it is wrong, and shouldn't have happened. Duncan's horses revert back to their most savage animalistic natures without the calming influence of their king and master (the implication is that so, too, will the people)
In nature, it is not only unnaturally dark, but storms and earthquakes occur. On the day following Duncan's murder, there is even an eclipse of the sun, and Lennox tells us that "darkness does the face of the earth entomb". This image of the earth being entombed by darkness suggests that the earth, and all who inhabit it are dead (if not physically then spiritually) or else, worse yet, not dead but buried in darkness.
The images of darkness suggests that a moral darkness has surrounded the land. When juxtaposed with the images of chaos in the animal kingdom, the audience fears that Chaos (Satan) reigns and has control over all of the land and its inhabitants, great and small.