In this scene Macbeth has killed the king and no one knows yet but Macduff was ordered by the king to wake him up (if he was still alive) but Macbeth is scared that Macduff will find out that he killed the king because he was the last person near the king so Macbeth would have been accused of treason and then Lennox finds out and accused the kings slaves and Macbeth managed to escape treason for now.  many people had seen king duncan a bloody corpse Macbeth and lady macbeyonly know what has happened because they organised the death of the king