False face must hide what the false heart doth know.

– William Shakespeare

Macbeth, Act 1, Scene 7. The last line of the scene contains the themes of deception, good vs evil, betrayal and appearance vs reality. Macbeth is saying that he and Lady Macbeth must act the part of loyal and friendly hosts to their guest King Duncan in order to hide their treacherous intentions of betraying and murdering him.