Why should Shakespeare's Macbeth have involved the witches?

Without the Witches, Shakespeare's Macbeth would have been a very different story.  The Witches are important for many reasons, but let's take a look at two very good reasons why they were involved.

1. The Witches provide one of three essential elements to the exposition of the play. In England when Shakespeare was writing plays, his audience would have expected that his plays begin with one of three elements: violence, sexual innuendo, and/or supernatural occurrences. This...

Without the Witches, Shakespeare's Macbeth would have been a very different story.  The Witches are important for many reasons, but let's take a look at two very good reasons why they were involved.

1. The Witches provide one of three essential elements to the exposition of the play. In England when Shakespeare was writing plays, his audience would have expected that his plays begin with one of three elements: violence, sexual innuendo, and/or supernatural occurrences. This last one--the three Witches--begin Macbeth, and Shakespeare's audience, regardless of class status, would have completely believed in the possibility of Witches (and consequently, their influence on people and situations).  The Three Weird Sisters "supernatural soliciting" would have drawn the audience in, but it also would have been very interesting to one audience member in particular: King James I (the King of England, who undoubtedly was present at the Globe Theatre when Macbeth ran).  He had written and published a very famous book about witchcraft called Daemonologie. Therefore, the Witches were socially relevant to the everyday lives of Shakespeare's audience AND a personal interest of the king himself.  Shakespeare was no fool--if the king was interested in and liked his play, shouldn't everyone?


2. Now on to the plot...Why are the Witches involved in the action of the story?  They provide a very interesting, debatable element for us, the audience: blame. Whose fault is it that Macbeth transforms himself from a war hero to a homicidal, self-involved tyrant by the end of the play?
   Lady Macbeth, you say?  She did give him quite a push at the right time, didn't she?  What about Macbeth, himself?  Well, that is another argument, and you'd have a valid point if you made it.  However, what if the responsibility for the entirety of Macbeth's problems stemmed from the Witches.  That complicates things a bit, doesn't it?  

   The Witches prompt us to consider whether Macbeth created his own fate or was doomed the very moment he stepped upon the heath with Banquo and received his first prophecy.  Remember, the Witches say in Act I, sc. i that the war will end soon and that they will meet Macbeth upon the heath.  Both of these comments show that they can foretell the future. The later prophecies (the Apparitions) prove this more fully. However, one could argue (as Banquo does prior to his death) that often 
   

   
   to win us to our harm,/The instruments of darkness tell us truths, Win us with honest trifles, to betray's/In deepest consequence.

   
   If Banquo is right, and the Witches are merely toying with Macbeth in order to make him do terrible things, then isn't he much more responsible for his own downfall than they?  

   For this reason, the Witches presence provides the audience (whether during Shakespeare's time or now) something to consider with regard to fault.