http://gallery.nen.gov.uk/gallery_images/0506/0000/0668/Macbeth_illustration14_001.jpg

Second Apparition:
Be bloody, bold, and resolute! Laugh to scorn
The pow'r of man, for none of woman born
Shall harm Macbeth.
4.1.79-81

Third Apparition:
Be lion-mettled, proud, and take no care
Who chafes, who frets, or where conspirers are:
Macbeth shall never vanquished be until
Great Birnam Wood to Dunsinane Hill
Shall come against him.
4.1.90-93

Macbeth:
Bring it after me.
I will not be afraid of death and bane
Till Birnam Forest come to Dunsinane.
5.4.58-60

From what the apparitions have told him, Macbeth's state of mind is now this: I'm invincible. He thinks that no one can kill him and that he has nothing to worry about. Macduff's army has disguised themselves with branches from Birnam Forest as they advance up the hill giving the illusion like the forest is moving closer to the hill as the apparition said could happen. Macduff and Macbeth fight one another when they meet finally and Macbeth is killed, Macduff was born through a c-section, not "woman born" as the apparition had said. Macbeth was too overconfident in himself in thinking that he was invincible and that nothing bad could possibly happen. This turned out to be his greatest flaw that lead to his demise.