Duncan is the kind of Scotland and Macbeth and Banquo have just received strange prophecies. Now Macbeth is convinced by Lady Macbeth to murder Duncan.
Yes, Macbeth has the prophecies. He seems to think that he should be king because he has been told that he is. He was basically told three things: He was Thane of Glamis, he would be Thane of Cawdor, and he would be king. Since the first was true and the second came true, he figures the third should be too.
Correction: Perhaps I might have been clearer if I had written "Shakespearean Cosmology" in my post #2 above. What I meant by the Shakespearean Cosmology is his belief and use of the great chain of being. Check out
Some reasons MacBeth would want to commit regicide and kill King Duncan:
1. To gain power over all of Scotland and advance his station in life.
2. To achieve the crown.
3. To fulfill the prophecy.
4. To look like a "man" in his wife's eyes.
Some reasons NOT to kill Duncan include
1. Murder is against natural law.
2. Killing a King will disrupt the Elizabethan cosmology and chaos would soon result.
3. Disorder, chaos, and unnatural acts will be loosed on the world.
4. The Weird sisters may not be a reliable source of information or prophecy. Why should he trust them?
5. Guilt and a stained conscience will inevitably result in psychological ailments.
Shakespeare had a very fertile mind and his fiction is renowned.
If I said, 'Macbeth never killed anyone' you are invited to prove me wrong. And since he lived a few hundred years before Elizabeth, I am at a loss to see that connection.