How do the tragic qualities of the play Macbeth contribute to the story's larger message?
The desire for power often leads to corruption. Depending on the situation, that corruption will manifest in different ways. Macbeth and Lady Macbeth conspire to make him king. The only way to do this is to kill Duncan. Just like one lie leads to another, Macbeth concludes he must keep on killing to protect his place in power. He is afraid of someone discovering his crimes and this fear is accompanied by his guilt which begins almost immediately after he has killed Duncan. The tragedies are the murders; plain and simple. You could also say that Macbeth’s transition from loyal subject to murdering tyrant was also a tragedy in itself and because it led to his and Lady Macbeth’s deaths.
The witches’ visions of the future could be prophetic or they might be suggestions. In either case, Macbeth is quick to believe in them, so he’s easily convinced to do the wrong thing. Notice that he’s also easily manipulated by Lady Macbeth. The tragic qualities, as in the tragic choices he and Lady Macbeth make, show how greed leads to corruption, corruption leads to crime, crime leads to fear and guilt and this leads to further crimes. Tragedy, corruption, fears and guilt all feed upon themselves. The cycle cannot be broken by more tragedy.