In Act V, Scene 5, the Messenger informs Macbeth that the trees are moving toward the castle. Macbeth is also informed that Lady Macbeth is dead. At this point, Macbeth feels he has no choice but to prepare for battle. He recognizes the movement of the trees as the prophecy of the Birnam Wood coming to the castle and sees no other way out than to fight.
In Act V, Scene 8, Macduff informs Macbeth that he (Macduff) was born by Cesarean section.
And let the angel whom thou still hast served
Tell thee, Macduff was from his mother's womb
Untimely ripp'd. (V.viii.18-20).
Macbeth says he will not fight Macduff because he realizes the other two of the witches' prophecies have come to fruition: "Beware Macduff" and Macduff is (technically) not of woman born. During lines 28-34, Macduff challenges Macbeth to surrender, further noting that Macbeth would then live to be an example of a tyrant. Macbeth, emboldened by the insult, counters this challenge by saying that he will not surrender to Malcolm nor be swayed by the will ("curse") of the people ("rabble") or Malcolm's loyal followers. This section confirms what we've already learned throughout the play. And that is that Macbeth had become a bloodthirsty tyrant and is, by this point, too stubborn and defiant to admit defeat; even in spite of the fact that all three of the witches' prophecies foreseeing his downfall have happened.
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