What are the themes in Act 2 and Act 3 of Macbeth?

In Acts 2 and 3 of Macbeth, Macbeth's
greed and ambition begin to take over his character as he tries to procure and protect
his title as king.  Macbeth now fully believes in the witches' prophecy, having been
given the title of Thane of Cawdor after returning from battle.  Macbeth then allows his
own thoughts and those of Lady Macbeth to cloud his good judgement.  He begins to
suspect that those close to him are dangerous to his position, and following his
interpretation of the witches' prophecy, Macbeth sees Banquo as an immediate threat. 
Thus, he decides to have Banquo and Fleance murdered.  Here, Macbeth's actions show that
uncontrolled greed and ambition may lead to one's downfall, a major theme in the play
overall.