What does Lady Macbeth adviseMacbeth to act like? Why?

Lady Macbeth knows that her husband is awful at pretending to be "normal" when under stress. She advises him to, "Look like the time. Bear welcome in your eye,. Your hand, your tongue. Look like th' innocent flower But be the serpent under 't." She wants him to look like the perfect host to Duncan but then strike when he is vulnerable.