Lady Macbeth: Then and Now

Then: Why do you make such faces? When all's done, you look but on a stool. 
Lady Macbeth is saying that because Macbeth saw Banquo's ghost and she doesn't see any ghost.
Now: I tell you yet again, Banquo's buried; he cannot come out on's grave. 
Lady Macbeth is now replaying the scene in her head, and telling Macbeth that it is impossible because Banquo is dead. That is how they are related because they are both about Macbeth seeing Banquo's ghost.