Mood

Greed is often associated with evil and dark aspects of one's mind and Shakespeare uses this when creating the atmosphere for Macbeth.  His descriptions throughout the entire play make is sound very bleek, which it is.  Greed is not a subject which can be properly protrayed if the mood is not right.  No one would see this play as a "cause and effect" piece of literature if it's mood was light, playful and happy.  Since the mood is very dark the readers seem to grasp the concept of evil that is evident in greed.
The mood is shown in the first scene of the play with the witches on the moor.  There is thunder, lightning, wind and rain and this is what it is like throughout the play.  The use of a "dark" mood can also be used as a method of forshadowing.  It gives us a feeling that something very bad and evil is going to happen and it does.  The murder of Duncan takes place on a particularly eerie night and it may seem that the weather is punishing Macbeth and Lady Macbeth for the actions they have done.