Final answer:
Upon finishing Macbeth's letter, Lady Macbeth decided that Macbeth was too kind to seize the throne through ruthless means, and resolved to manipulate him to murder King Duncan.
Step-by-step explanation:
After reading Macbeth's letter in William Shakespeare's tragedy 'Macbeth', Lady Macbeth concludes that her husband, Macbeth, is too kind-hearted and 'full of the milk of human kindness' to achieve their ambitious aspirations. Furthermore, she understands that the prophecy declared by the witches, which states that Macbeth will become king, will only come true through treachery and deceit. She determines to convince him to murder King Duncan, by using her own manipulative and ruthless nature.
Learn more about Macbeth