Perhaps the most moving and horrifying passage in Macbeth is Lady Macbeth's soliloquy of Act I, Scene 5. Prior to this speech, she reads the letter from her husband that describes Macbeth's encounters with the three evil sisters of the preternatural world. Lady Macbeth's first reaction to this missive is her expression of concern that her husband's nature will preclude him from acting upon the witches' predictions.
....Yet do I fear they nature;
It is too full o' th' milk of human kindness
To catch the nearest way. Thou wouldst be great,
The illness [wickedness] should attend it. (1.5)
Therefore, in order to impel her husband to pursue the path of becoming king, Lady Macbeth invokes the preternatural world herself, asking the spirits to take away her womanhood so that she be not weak in purpose. Further, she implores these spirits of evil to harden her against any sympathies or pity and to change her "milk of human kindness" to bitterness.
....Come, you spirits
That tend on mortal thoughts, unsex me here,
And fill me, from cown to the toe, top-full
Of direct cruelty! Make thick my blood,
Stop us th' access and passage to remorse
That no compunctious visitings of nature
Shake my fell purpose, nor keep peace between
Th' effect and it! (1.5.)
Lady Macbeth's supplication to be man-like equates masculinity with violence and belligerence. Having thus hardened herself against emotion, she is emboldened except when Duncan resembles her father "as he slept." Nevertheless, she scolds Macbeth after he assassinates Duncan, telling him,
A little water clears us of this deed:
How easy is it then! (2.2)
and she urges Macbeth to simply put on his nightclothes in case they are discovered to have been up all night. Then, in Scene 3, she feigns horror and sorrow that Duncan has been killed when Macduff informs them of what he has discovered. Later, in Act III, Scene 4 as Macbeth's conscience disturbs him so much that he imagines Banquo's ghost, the then unconscionable Lacy Macbeth chides her husband, "Are you a man?" and tells him that the "fit is momentary" and in a moment it will pass.