What power do the three witches in Macbeth seem to possess? What do they prophesy will happen to Macbeth and Banquo?

In Macbeth, the witches have the power to present events that are fated to occur. When Macbeth and Banquo first meet the witches when they are returning from the battlefield, the witches tell Macbeth that he is the Thane of Glamis, will soon be the Thane of Cawdor, and will be King hereafter. They tell Banquo that he is lesser than Macbeth yet greater because although he will not be King, he will be the father to a line of kings. Later in the play, Macbeth purposely seeks the witches for a second prophecy, and they tell him to beware Macduff, to not fear of any who is born of woman, and to not fret until Birnam Wood comes to Dunsinane. Macbeth misinterprets most of the second prophecy, feeling that he is invincible, but because the witches are only harbingers of fate and destiny, the prophecies all eventually come true, and Macbeth meets his downfall.