The scene starts with Lady Macbeth reading Macbeth’s letter. She felt as if her husband is not evil enough to be that much ambitious. And this scene is all about showing how much evil is Lady Macbeth.

LADY MACBETH

     O, never
Shall sun that morrow see!
Your face, my thane, is as a book where men
May read strange matters. To beguile the time,
Look like the time. Bear welcome in your eye,
Your hand, your tongue. Look like th’ innocent flower,
But be the serpent under ’t. He that’s coming
Must be provided for; and you shall put
This night’s great business into my dispatch,
Which shall to all our nights and days to come
Give solely sovereign sway and masterdom.

SparkNotes Editors. “SparkNote on Macbeth.” SparkNotes.com. SparkNotes LLC. 2002. Web. 27 Sept. 2016.