Final answer:
Lady Macbeth's request to the 'spirits that tend on mortal thoughts' indicates her desire to become more ruthless and cruel in order to carry out the plan to murder King Duncan.
Step-by-step explanation:
Lady Macbeth's request to the 'spirits that tend on mortal thoughts' to 'unsex' her and to 'come to my woman's breasts, and take my milk for gall' indicates her desire for a transformation. She wants to rid herself of femininity and become more ruthless and cruel in order to carry out the plan to murder King Duncan. By asking the spirits to take away her feminine qualities, she hopes to become more like a man, who was traditionally associated with power and aggression in that era.