Examine the role of supernatural in the play Macbeth. To what extent does it lead to Macbeth, Lady Macbeth and Scotland's decline ? I want to write...

Analyzing the effects of the supernatural elements in
Macbeth is a good approach to the play.  You might begin by looking
at the witches' prophesies to Macbeth and Banquo at the beginning of the play.  The most
important of these is the prophesy that Macbeth will become king and that Banquo's sons
will be kings.

Predicting the future is a supernatural act,
but mere humans make these prophesies come true.  Macbeth and Lady Macbeth, upon hearing
the witches' prophecies (Lady Macbeth through her husband's letter), decide that it is
Macbeth's fate to become king.  So they take the "near'st way" to this position by
murdering Duncan.  It is Macbeth's and Lady Macbeth's belief in the truth of the
prophesies that propels them to murder.  Instead of letting the prophesies come true on
their own, they make them happen. And, of course, Macbeth makes a very poor king indeed,
creating chaos in all of Scotland.

You then might look at
Macbeth's second encounter with the witches.  They again predict the future.  This time
Macbeth's reaction is quite different.  Instead of acting to fulfill the prophesies, he
acts to prevent them.   Macbeth now believes that he can change his
fate.

So, you might view the witches as having several
roles:  that of instigators, temptors, and prophets.  But clearly the decision to murder
is Macbeth's and Lady Macbeth's.