In this scene, Lady Macduff is upset that her husband has run away to evade Macbeth. Her son comes in, and she has a conversation with him. She tells him that his father is dead, which isn't true. She asks him how he is going to live without a father. He says he will live like a bird, finding whatever he can to eat. He also tells her he knows his father isn't dead.

The son asks if his father is a traitor. His mother says yes. The son asks what a traitor is. Lady Macduff responds that it is someone who swears to something but is lying about it. Her son asks what happens to traitors, and his mother says that they must be hanged. When the son asks who will do the hanging, the mother replies, "the honest men."

At this point, the son shows he perceives how corrupt Scotland has become under Macbeth, for he says:

Then the liars and swearers are fools, for there are liars and swearers enough to beat the honest men and hang up them.

The son's insight is that the world as he knows it is full of liars and swearers: the evil men outnumber the honest and just, so evil forces can beat and hang the innocent. In other words, injustice rules because it has the power.

This foreshadows the injustice that is due to come in just a few minutes as Macbeth's assassins enter and murder Lady Macduff and her children.