In Act IV, Scene One, Macbeth once again visits the witches. He is concerned because he wants his sons to succeed him, not Banquo's The witches deliver three new prophecies.
The first witch tells Macbeth to beware of Macduff:
Beware the Thane of Fife.[Macduff]
The second promises that no man "given birth to by a woman" shall harm Macbeth. This seems like Macbeth has nothing really to fear because, he reasons, all men are born from women.
The third witch presents an ghostly image of a child wearing a crown who is holding on to a tree, The ghost promises:
Macbeth shall never vanquished be until Great
Birnam Wood to high Dunsinane Hill shall come against him.
Macbeth replies that could never happen because no one can cause a forest to move.
However, Macbeth is still concerned about Banquo and
asks, "shall Banquo's issue ever/Reign in this kingdom?" In other words, will any of Banquo's children ever be king of Scotland? So the witches show Macbeth a line of kings. The last king holds a mirror which, in Shakespeare's day, probably reflected the image of James I, who traced his ancestry through Banquo. Today, the image usually reflects the face of Banquo.
The witches then disappear as Lennox enters the room to tell Macbeth that Macduff has fled to England and Macbeth announces plans to kill Macduff's family.