The first set of predictions, or prophecies may start the action of the tragedy in motion, but the second prophecy seals Macbeth's fate.
In Act IV, Scene I, Macbeth visits the witches, he demands information about his future. This second prophecy leads Macbeth to be more paranoid and results in his ordering the deaths of Macduff's family.
The witches makes four mysterious predictions, that are more like warnings for Macbeth's future as king.
The first: Beware the Thane of Fife, Macduff.
The second: "The power of man, for none of woman born Shall harm Macbeth." (Act IV, Sc I)
The third: "Who chafes, who frets, or where conspirers are:Macbeth shall never vanquish'd be until Great Birnam wood to high Dunsinane hill
Shall come against him."
The fourth: "A show of Eight Kings; the last with a glass in his hand: BANQUO'S Ghost following."
"Macbeth is out of control and reacts without thought to his actions. He feels he must spill blood to remain in control and powerful. Once again Macbeth has innocent blood on his hands, and again, he feels no remorse. He is driven by his lust to control the situation and flex his power."