Before hearing this, Macbeth was pretty content with his life. Now he has horrible imaginings, ones that befit a traitor more than a war hero. Though he isn't exactly excited about murdering Duncan, he doesn't wholly dismiss the prospect.
Macbeth frames Duncan's guards with his wife's help, casts suspicion on Duncan's sons, and takes the crown for himself. The King's sons Malcolm and Donalbain have disappeared, and no one questions Macbeth's loyalty or his guilty conscience.
With his head fresh in the crown, Macbeth feels unsafe in his newly found power until the one remaining threat is removed. Though Banquo has not cast any suspicion nor been unkind in any way, it seems best to have him (and his son Fleance) murdered – just in case. Macbeth has to ensure that he hasn't sold his soul for Banquo's gain.
Banquo's ghost throws Macbeth into a public and embarrassing fit. That same night, Macbeth has received intelligence that Macduff, Thane of Fife, has gone to England to gather forces with Malcolm and Siward.
The weird sisters have given Macbeth artificial intelligence that fosters false hopes of victory in him. Macbeth's destruction lies in the fact that the prophecies come true to the rebels' advantage instead of Macbeth's. Macbeth, in a sudden burst of perception, realizes he is defeated. With his wife freshly dead and his faith sorely missed, Macbeth dies fighting. He leaves the play a warrior content with his lot – just as he entered it.