Absolute power corrupts absolutely… unless, of course, your absolute power is a god-given right. In Shakespeare's time, the Divine Right of Kings was the idea that the power of kings comes directly from God. Guess who was a big fan of the Divine Right of Kings? Our man Will's very own patron, James I. In Macbeth, power is natural—until it's not. When Macbeth kills Duncan, he goes against the very law of nature and God by killing his king, and then gets killed in return. According to the play, it's okay to kill King Macbeth because King Macbeth is actually a tyrant. But who gets the power to decide what tyranny looks like?
Although King Duncan is a good man and a virtuous king, he's too "meek" to rule effectively. Macbeth, on the other hand, rules Scotland like a tyrant. The play, then, suggests that a truly good monarch should be strike a balance somewhere between Macbeth and Duncan.