In Macbeth, what is ironic about the Witches' second predictions?(Macbeth shouldn't fear anyone born to a woman and Great Birnam Wood to High Dunsinane Hill)
Both of these predictions are ambiguous. Macbeth interprets them as positive omens, believing that everyone is born of woman and that no forest can move up a hill. The witches, however, are tricking Macbeth into a false sense of complacency with these predictions; he thinks he is safe.
In Act 5 Macbeth discovers to his surprise that Great Birnam Wood does indeed seem to be moving up High Dunsinane Hill to the castle when Malcolm directs the soldiers to camouflage themselves with branches from the trees to hide their numbers. Despite this setback, Macbeth continues to be sure he is invincible until he faces Macduff in battle and Macduff announces that he was "untimely ripp'd from his mother's womb," meaning that he did not arrive by a normal delivery from his mother.
Both of these predictions seemed to Macbeth to prove that he would not be defeated, yet ironically both actually told the truth. He was defeated after the forest "moved" up the hill, and Macduff was not "born of woman." Macbeth did not expect either of these prophecies to be true.