We all turn to Terry Eagleton to tell us what MacBeth, and indeed everything else, is about. Eagleton has changed his mind. As a young Marxist literary critic, Eagleton saw the three witches as revolutionaries, libertarians who attacked the established political order. Now, as a slightly older and wealthier Marxist, Eagleton has no time for the witches. They're nihilists that care about nothing and champion destruction for its own sake. They rubbish everything and add nothing, much like some blogs do.
Gnostics, who were wrong Christians, thought that matter was evil. Good, proper, right, orthodox Christians like Saint Augustine and me, realised that evil is nothing - it is the absence of anything. It's vacuous, empty and meaningless. That's why Christianity never mentions the devil, or demons or anything like that, since they would be the embodiment of evil and therefore something, not nothing. Some enraged lunatic wielding a chain saw is therefore not evil. The third reich, the inquisition, the gulags and the killing fields, since they actually existed, were not evil.
This is the kind of insight into the nature of evil that only Terry Eagleton, Saint Augustine and me can bring.
So in conclusion, remember to use your vote wisely this polling day.