ambition seems—at least at first—to be more powerful than his. In the lines you cite, she expresses her concern that Macbeth is not ruthless enough to take thenearest way, or the shortest and quickest path, to the throne. Lady Macbeth does not want to wait years for Duncan to die and for something to happen to Malcolm. She wants Macbeth to be king now, and she wants him to want it as badly as she does. Thus, her statement shows us just as much about her character as it does about her husband's. She thinks of him not so much as a good man but as a weak man—she thinks he will be bound by ties of kinship and loyalty (something she seems to associate with femininity or femaleness, as we learn later when she prays to be "unsexed" and remorseless) and that he will refuse to consider how he might push the prophecy forward, making it come true now rather than waiting years.

Interestingly, Lady Macbeth is wrong on this point; Macbeth has already considered the murder of Duncan before he gets home. Based on his actions for the remainder of the play, Lady Macbeth's statement that his character "is too full o' th' milk of human kindness" shows that, perhaps, she does not understand her husband nearly as well as she thinks she does. It is possible that her lack of understanding, and her underestimation of Macbeth's own ability to be cruel, is what creates the tension that results in her later sleepwalking, apparent guilt, and eventual suicide.

Lady Macbeth is not talking to her husband but is thinking aloud. Her soliloquy is all about his ambition, but she knows him well and understands that he is not sufficiently ruthless to use treachery and violence to obtain what he wants. He is too soft-hearted, in her opinion. That is what she means by "the milk of human kindness." It is an apt metaphor for a woman because it suggests the feeling of a women breast-feeding a baby. It is also a veiled insult when applied to a man. Right after that statement she says, "Thou woulds't be great, / Art not without ambition, but without / The illness should attend it." By "illness" she means ruthlessness. There is no question that Macbeth is ambitious, but his wife is afraid that he is not sufficiently ambitious to do what he has a golden opportunity to do that very night when Duncan and his two sons will be their guests. She concludes this soliloquy by wishing her husband would hurry home so "That I may pour my spirits in thine ear / And chastise with the valor of my tongue / All that impedes thee from the golden round [the crown]." Shakespeare seems to be trying to present Macbeth, not as an evil man like Richard III or Iago, but as a good man gone wrong because of outside influences, including especially his wife. It is interesting that this is a soliloquy but is presented as if she is speaking to her husband. She seems to be practicing, preparing for what she intends to say to him when he arrives. She also reveals that they have discussed these matters before. She reveals both her own character and her husband's in this soliloquy.

This quote establishes Lady Macbeth's own ruthless nature and helps foreshadow the later role she would play in the eventual murder of Duncan, castigating and shaming Macbeth when he suffers a crisis of conscience to ensure that he goes through with the plot. In the process, it establishes an impression of Lady Macbeth's relationship with her husband as being (by all accounts) the more ruthless of the two, at least in this part of the play.

However, what I find particularly interesting is the question of how this statement fits into Macbeth's larger plot, particularly as it involves Macbeth's deterioration into a bloodthirsty tyrant. After all, as we proceed further into the play, we notice that Macbeth's rule has a deeply sanguinary nature. In a way, I think Macbeth is a deeply psychological play, one which examines how this act of murder affects its perpetrators. We see this reflected in Lady Macbeth's later madness and suicide brought on by guilt, and I think we see this in the bloodthirsty tyranny of Macbeth himself. Thus, when seen within that context, this statement helps to establish an initial impression of Macbeth that this later characterization can be contrasted against. Thus it suggests the degree to which Macbeth himself has fallen, as he twists himself into a monster.

This quote comes from Act I, Scene V and is significant because it reveals much about Lady Macbeth's character and the relationship she has with her husband. Firstly, by stating that Macbeth is full of the "milk of human kindness," Lady Macbeth argues that her husband is naturally a kind and gentle person—so much so that he cannot "catch the nearest way" (to take what he wants through force).

By making this judgment about her husband, Lady Macbeth reveals an important trait of her own: that she is the natural leader in their marriage. She knows that she must take charge of this situation, or else Macbeth will lose his chance to be king. In other words, it is down to her to make sure that this natural kindness is replaced by ambition and violence, traits which she has in abundance.

Through this quote, Shakespeare inverts the natural order. Instead of adopting the traditional masculine and feminine roles, the roles of Macbeth and Lady Macbeth are reversed. It is she who leads the way, and it is he who will follow.

Lady Macbeth says this line immediately after reading a letter she has just received from her husband.  In that letter, Macbeth informs his wife that the witches have prophesied that he will be King.  He is telling Lady Macbeth the news so that she might share in the joy that the prophesy has brought him, saying,

"This have I thought good to deliver thee my dearest partner of greatness, that thou mightst not lose the dues of rejoicing by being ignorant of what greatness is promised thee...Lay it to thy heart..." (I,v,10-13).

Lady Macbeth is indeed overjoyed, and in her excitement she reveals herself to be an extremely ambitious and unscrupulous woman.  Her first inclination is to take things into her own hands, doing whatever it might take to make the prophesy come true, and come true as quickly as possible.  To this end, she schemes to do away with Duncan, the current King, but she is afraid that Macbeth, although ambitious, is not as ruthless as she is.  She is afraid that he is too kind by nature to do what needs to be done so that he can be King right away, and she voices her concern, saying,

"Yet do I fear thy nature, it is too full o' the milk of human kindness to catch the nearest way.  Thou wouldst be great, art not without ambition, but without the illness should attend it" (I,v,16-20).

Lady Macbeth knows her husband is ambitious, but she is afraid he doesn't have the "illness", or the unscrupulous disregard for goodness, to act heinously and kill Duncan to gain the crown for himself.