What are the main themes in Macbeth, and why?
These are some of the main themes in Macbeth:
a) ambition: Macbeth refers to his 'vaulting ambition' in his soliloquy in act1 sc.7. His ambition to become the king of Scotland is exteriorised by the witches' prophecies in act1 sc.3. Lady Macbeth's more selfless ambition goads Macbeth to the path of crime.
b) battle between fair and foul: this battle is primarily fought out in the soul of Macbeth, and in the Malcolm-led offensive that ends the reign of terror.
c) kingship: We have four kings and their rule(s)--good old Duncan killed by Macbeth who becomes the usurping king unleashing a reign of terror, the absentee king of England who is a great healer of his people, and the new king, Malcolm, ushering a new era of justice and sympathy.
Besides these, we may also look for such other themes like murder & bloodshed, madness, treachery, appearance & reality, fear etc...