In Shakespeare's play, Macbeth, the following quote is spoken by Lady Macbeth:

"Was the hope drunk / Wherein you dressed yourself? hath it slept since? / And wakes it now, to look so green and pale / At what it did so freely?" (I, vii, 36-40)

After the witches' predictions have proven true—when Macbeth unexpectedly becomes the Thane of Cawdor—the rest of the prediction ("...that shalt be king hereafter," I, iii, 50) begins to eat not only at Macbeth's mind, but also at his wife's. Lady Macbeth is a conniving and ambitious woman: she wants to be queen, and at the beginning of the play, she has no qualms about what they need to do between them to make it happen.

At the beginning of the scene, we see the last vestiges of Macbeth as he was at the start of the play: the heroic, valiant and loyal servant of Duncan. He has had time to think of their plans to murder Duncan (the king), while the older man visits with them. He tells his wife:

We will proceed no further in this business:
He hath honor'd me of late, and I have bought
Golden opinions from all sorts of people,
Which would be worn now in their newest gloss,
Not cast aside so soon. (lines 31-35)

Macbeth is having second thoughts. He loves Duncan. Duncan is his King; and Duncan is his cousin. [The man is also enjoying Macbeth's hospitality, and it was a long-standing rule of war that if someone came under your roof—even an enemy (which Duncan is not), his (or her) safety was guaranteed. Only a man without honor would do his guest harm.] In addition, Macbeth reasons, Duncan has recently rewarded him, and he has been praised by many people for his actions in battle. While all this is still new, he does not wish to do away with it so quickly, but enjoy it.

Lady Macbeth knows how to manipulate her husband. She belittles him and questions his courage and his manhood. She responds to his desire to wait, saying:

Was the hope drunk
Wherein you dress'd yourself? Hath it slept since?
And wakes it now, to look so green and pale
At what it did so freely?

Lady Macbeth is asking him what drunken state of mind (likened to casually putting on clothing) was he in when he agreed to commit the murder? And since that time, has his drunkenness worn off, making him sick (green) from a hangover so that in the light of day, with a clearer mind, he cannot follow through?

She suggests with the image of clothing that Macbeth is "infirm of purpose," unable to commit himself; he changes his mind like people change their clothes. She is insulting him for his inconstancy.

She then pulls the "love" card:

From this time
Such I account thy love. (lines 38-39)

Basically she says, well from now on, I know how much you really love me. (She is bitingly sarcastic, and she makes his desire to maintain his ethical base a choice: do it your way, or show me you love me.)

The use of the clothing imagery is given to allow Lady Macbeth to argue with her husband that he was never serious about their plan if he can change his mind as quickly, easily and thoughtlessly as one changes his/her clothes