After reading Macbeth's letter, Lady Macbeth's reaction indicates that she knows her husband's nature very well. Her view of his character is that he does not lack ambition, but that he lacks the ruthlessness (the evil) necessary to gain power quickly through Duncan's murder. She believes that Macbeth will be afraid to murder Duncan, but that once Duncan is dispatched, he will be glad and would not regret that it happened. Lady Macbeth knows what she must do to spur Macbeth into murder in order to gain the crown, and she is well prepared to do it, to "chastise with the valor of my tongue / All that impedes [Macbeth] from the golden round."
We learn nothing of Macbeth's nature from her response to his letter; we do, however, learn what Lady Macbeth thinks of her husband--and her view of him may or may not be true. In any case, Lady Macbeth's reaction to the letter tells us about Lady Macbeth's nature.
We learn of Macbeth's nature from Macbeth's words.
Macbeth informs his wife, Lady Macbeth of the prophecies he had received from the witches that predicted he would become Thane of Cawdor and then will be king hereafter, through a letter. He tells her that the treacherous Thane of Cawdor had been stripped of his title and Macbeth had replaced him as Thane of Cawdor just as the witches had prophesised. After reading the letter, Lady Macbeth is also taken in by the prophecy of the witches. However she is aware that there is a high probability that it will not be as easy for Macbeth to become King of Scotland as it was for him to be Thane of Cawdor. She knows Macbeth will have to kill to get to that position. Knowing her husband’s nature well, she also comes to the realisation that her husband is incapable of murder. Although she knows he does not lack the ambition, she does know he lacks the ruthlessness that is needed to commit to an act of evil. ‘…yet I do fear thy nature, it is too full o’th’milk of human kindness…’ So she calls upon spirits to make her strong enough for her husband, and for her to embody the evil that is needed for Macbeth to reach his ambitious goal. She claims to want to be morally misguided so she does not hesitate in allowing her husband to kill. “That my knife see not the wound it makes, Nor heaven peep through the blanket of the dark, to cry ‘Hold, hold.” After exclaiming this, she is now ready to guide Macbeth to make whatever choices he has to, to take fate into his own hands and reach his ambitious goal of becoming the king of Scotland.