Then suddenly, everything changes. This loyal general's ambition is suddenly revealed, and it is quickly seen that he is swayed by superstition and predictions of fortune. The three witches quite easily gain control over his will and desires - indeed, they barely even have to try. Almost before we know it, the brave MacBeth has turned into a man guided by ambition and yet uncertain. In the lead-up to his murder of King Duncan, he changes his mind many times and wrestles with his conscience. He is morally unstable. Eventually, he makes up his mind. The speed in which MacBeth the hero becomes MacBeth the murderer is quite startling.
It also must be noted that despite (or perhaps because of) his moral instability, he is a deep thinker, and he clearly understands that killing Duncan is not like slaughter on the battlefield. At wartime, he is fighting his enemies, people who aim to subjugate his nation and kill his people (even himself). I doubt he even sees his opponents as human. However, murdering Duncan is just that - murder. There is a vast difference between killing during a war and killing a man lying asleep in his bed. Too few people even seem to realise this, and I'm starting to tire of hearing "If MacBeth can kill so easily on the battlefield, why can't he kill Duncan?"
There are some thoughts for now. Agree? Disagree?