“That won’t work because there are more liars than there are honest men.” Who said this to whom? What does it suggest about this...

Your question refers to the conversation that takes place between Lady Macduff and her young son in Act 4, Scene 2, just before the Murderers arrive with orders from Macbeth to kill Macduff's family and everyone else in his castle.

SON: Was my father a traitor, Mother?

LADY MACDUFF: Ay, that he was.

SON: What is a traitor?

LADY MACDUFF: Why, one that swears and lies.

SON: And be all traitors that do so?

LADY MACDUFF: Everyone that does so is a...

Your question refers to the conversation that takes place between Lady Macduff and her young son in Act 4, Scene 2, just before the Murderers arrive with orders from Macbeth to kill Macduff's family and everyone else in his castle.

SON: Was my father a traitor, Mother?

LADY MACDUFF: Ay, that he was.

SON: What is a traitor?

LADY MACDUFF: Why, one that swears and lies.

SON: And be all traitors that do so?

LADY MACDUFF: Everyone that does so is a traitor and must
be hanged.

SON: And must they all be hanged that swear and lie?

LADY MACDUFF: Every one.

SON: Who must hang them?

LADY MACDUFF: Why, the honest men.

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

This dialogue between mother and son is intended to show the loving relationship that exists between them. It also characterizes the boy, who must be only about ten years old, as intelligent and likeable. We can understand why his mother loves him. The audience is amused, and there will be a lot of laughter at the boy's observation that there are more liars and swearers than honest men. Out of the mouths of babes! The author's intention is that the mother and little boy should be taken by complete surprise when the Murderers appear so abruptly. The audience is also taken by surprise, even though they were forewarned by Macbeth when he says in an Aside in Act 4, Scene 1:

The castle of Macduff I will surprise,
Seize upon Fife, give to th' edge of th' sword
His wife, his babes, and all unfortunate souls
That trace him in his line.

The key word here is "surprise." Since Macbeth says he intends to take the castle of Macduff by surprise, the intrusion of Macbeth's soldiers should come as a surprise to mother, son, and audience simultaneously. Shakespeare achieves this surprise effect by preceding the incursion with some deliberately misleading and comical dialogue. Macbeth probably says that he intends to take the castle by "surprise" because he only sends a small group of men to execute his orders, and they could only get inside if they took the castle by complete surprise.

The son shows remarkable bravery in spite of his small size and tender years. The kinds of questions he asks his mother show he cannot be much older than ten. He is forced to take on the role of protector which Macduff would have had to assume if he had been there. The little boy is true son of a brave and noble father. The audience feels the loss Macduff will have to bear before Macduff himself ever hears about what Macbeth has done to his family.