Reasons why Lady Macbeth wants Macbeth to kill Duncan.
The reason Lady Macbeth encourages her husband to kill King Duncan is because she is motivated by her ambition and desire to become queen. After Lady Macbeth reads her husband's letter regarding the prophecy of the three witches, she commands evil spirits to make her callous, bloodthirsty, and courageous enough to plot Duncan's murder.
Lady Macbeth is excessively ambitious and desires the authority, prestige, and material wealth that come along with being queen, which is why she wants her husband to kill King Duncan. However, Lady Macbeth is worried that her husband is too kind and sensitive to follow through with assassinating the king. Therefore, Lady Macbeth plans and participates in the plot to kill King Duncan to guarantee that she will become queen. Unfortunately, Lady Macbeth's plans are in vain because she gradually becomes overwhelmed with guilt after Macbeth kills King Duncan. Despite becoming queen, Lady Macbeth ends up losing her mind and commits suicide by the end of the play.