Elizabethans believed in an ordered universe. In other words, everything could be ranked -- like a military -- in a clear, easily explained order. In part, this was due to an underdeveloped scienctific rationale which resulted in an overly simple world-view. When order was broken, everything underneath the point of conflict became disordered as well.
In this sense, Macbeth was the point of conflict or the element which caused disorder. Examine the order in the play before Macbeth killed Duncan, after he killed Duncan, and then when Macbeth was killed. Pay special attention to how the events and actions were ordered during each of these times.
For one thing, according to tour guides in Inverness, Scotland, the fact that Elizabeth was queen during Shakespeare's time was responsible for the bard's portrayal of the king as evil when in fact Macbeth was much crueler and malicious. Because Duncan was a Scot, Shakespeare wrote his play to be more "politically correct"; in fact, Macbeth has been labeled a "sympathetic tragic hero" by some critics.