Though Macbeth does not appear in Act IV, scene iii, we glimpse his effect upon his kingdom, and the future of Scotland is foreshadowed.
Act IV, scene iii may be the first time we see an honest conversation in the entire play. I say "may be" because it is unclear whether or not Malcolm is really testing Macduff's loyalty. Maybe he's testing his disloyalty. Some critics (Snyder) think Malcolm will be an even worse tyrant than Macbeth.
This tyrant, whose sole name blisters our tongues,MACDUFF MALCOLM
Was once thought honest: you have loved him well.
He hath not touch'd you yet. I am young;
You may deserve of him through me, and wisdom
To offer up a weak poor innocent lamb
To appease an angry god.But Macbeth is.MACDUFF
A good and virtuous nature may recoil
In an imperial charge. But I shall crave
That which you are my thoughts cannot transpose:
Angels are bright still, though the brightest fell;
Though all things foul would wear the brows of grace,
Yet grace must still look so.
Macbeth is called "treacherous," "an angry god," "a tyrant," and "the evil." His betrayal of Scotland has left all his Thanes reeling, questioning each others' allegiance. Even Macduff's son, in the scene before, says there are more dishonest men in the kingdom than honest ones.
Can we trust Malcolm here? Can we trust Macduff, for that matter? Macduff's wife calls him a "traitor" before she dies. Even Macduff calls himself "sinful Macduff." Is there no hope for Scotland? The country bleeds.
Later, Macduff will learn that his wife and son have been murdered. Macbeth is now killing women and children, civilians. This supports all the claims by Malcolm against Macbeth: he is the evil.
In Act IV, Scene iii Malcolm and Macduff have arrived in England and they are about to have an audience with the King of England. They are seen in conversation just outside the King of England's palace. Both of them discuss the ever increasing tyranny and cruelty of Macbeth as he brutally destroys both Scotland and its people. Macduff remarks sorrowfully:
Malcolm remarks very tellingly that Macbeth is so cruel that as soon as one mentions his name that person's tongue gets scorched with blisters:
This is proved true at the end of the scene when Ross reports to Macduff that Macbeth has slaughtered mercilessly his helpless wife and children, leading us to agree with Macduff that even in hell there cannot be a more wicked devil:
From Act IV Sc 3 we learn that Macbeth is not only corrupt and evil but is also capable of carrying out horrendous deeds to achieve his aim.
The function of this scene is to discuss and assess the moral forces of the play before the final attack on Macbeth's corruption and treachery is set in motion. The main discussion takes place between Malcolm,the murdered king's son and heir to the throne and Macduff .a loyal nobleman. During the discussion Macduff says:
Not in the legions
Of horrid Hell can come a devil more damn'd
In evils to top Macbeth (Act IV Sc 3 L 57-59)
In his reply Malcolm says:
I grant him bloody,
Sudden,malicious,smacking of every sin
that has a name. (Act IV Sc 3 L 58-61)
The horrors of Macbeth's reign are discussed and analysed as well as the affairs of the realm. We learn that Malcolm and Macduff are both honourable men. The fact that they consider that there are no bounds Macbeth's treachery confirms to us the evil of his ways
Their conclusion is proven correct when at the end of the scene Ross announces that Macbeth has had Macduff's wife and children mercilessly murdered.