They met me in the day of success; and I have learned by the perfectest report, they have more in them than mortal knowledge.........
Come, you spirits that tend on mortal thoughts, unsex me here, and fill me from the crown to the toe top-full of direst cruelty
Act II, Scene II
Who was it that thus cried. Why, worthy thane, You do unbend your noble strength to think so brainsickly of things. Go get some water, and wash this filthy witness from your hand.
Still it cried, “Sleep no more!” to all the house. “Glamis hath murdered sleep, and therefore Cawdor shall sleep no more. Macbeth shall sleep no more.”
While her husband is tempted by the witches, Lady Macbeth asks evil spirits to possess her. These spirits are 'murdering ministers', who will strengthen her will and harden her heart. Their main function, as she sees it, will be to deprive her of any natural feelings of kindness that might weaken her murderous intent. She will then be capable of organising the murder of Duncan without being troubled by a guilty conscience