At Inverness, Lady Macbeth reads a letter in which Macbeth tells her of the witches' prophecy. Lady Macbeth worries Macbeth is too kind and honorable to fulfill his ambition and the prophecy. She decides to question his manhood to make him act.
Lady Macbeth is established as power-hungry. She sees honor as a weakness, and knows how to push her husband's buttons: question his courage.
A servant enters with news that Duncan will spend the night, then exits. Lady Macbeth says Duncan's visit will be fatal, and calls on spirits to "unsex me here… and take my milk for gall" (1.5.39-46).
In order to murder Duncan, Lady Macbeth not only renounces her womanhood, she literally asks to be turned into an unnatural fiend!
Macbeth enters, and says Duncan will spend the night and leave the next day. Lady Macbeth says Duncan will never see that day. She counsels Macbeth to look like an "innocent flower," but be the viper hiding beneath it (1.5.63). Macbeth remains unconvinced. Lady Macbeth tells him to leave the plan to her.
Macbeth is still struggling against his ambition. Lady Macbeth's advice on how to hide one's true intentions involves exploiting nature. (Note: in the Garden of Eden, the devil hid himself in the form of a snake.)