This scene plays a very important piece of the play. This is when we see how cold hearted and evil Macbeth is, and also how this action that Macbeth performs will change the outcome of his life later on in this play. For this scene Macduff swears revenge on Macbeth and as we know this is why Macbeth dies in the play.
In this scene Lady Macduff and Macduff's son are arguing on why Lady Macduff believes that her husband is a traitor and deserves the worse punishment. She believes that Macduff left them unprotected without caring of their well being, which turns out to be some what true. The son of Macduff, even do his age was too young to understand, believes otherwise of his dad and defends him until his death.
The Lady Macbeth and her son receive a very strange and unexpected visit from an unknown man which tells them that they are in danger and that they should leave somewhere safer. The message, as important as it is, was treated like a joke by Lady Macbeth which we know must have regretted it.
The murders appear and kill all of Macduff's family leaving no one alive. When Macduff receives the message he gets raged and swore to kill Macbeth. This is how the fate of Macbeth is written and how Macbeth kind of wrote his own death warrant by doing a point less evil act of greed and lust of power. Macbeths power went so high into his head, which he couldn't keep control of it and finally ended with his life.
This scene is the one where the fate of Macbeth's life is written. Also shows how paranoid and insane he is becoming, which is somewhat something that takes some blame off Macbeth's back. The witches have most of the faults because Macbeth was a normal and week-minded guy who never thought of murder. But the greed and too much power changed his life for ever.