In Act I scene 5 Lady Macbeth reads a letter from her husband where he explains to his wife the predictions the three witches have old him and Banquo. His letter doesn't only show the audience his ambitions for power, but Lady Macbeth's ambitions as well.
Lady Macbeth is excited by the titles the witches have seen in his future, but worries that he may not be manly enough to rise to the occasion and do what will be needed to make all of their predictions come true. She believes that while he has the ambitions, he is going to have to overcome his lack of mean nature.
I fear thy nature;
It is too full o' th' milk of human kindness
To catch the nearest way: thou wouldst be great,
Art not without ambition, but without
The illness should attend it. What thou wouldst highly,
That wouldst thou holily; wouldst not play false,
And yet wouldst wrongly win. Thou'ld’st have, great Glamis,
That which cries, “Thus thou must do,” if thou have it,
And that which rather thou dost fear to do,
Than wishest should be undone. Hie thee hither,
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,
Which fate and metaphysical aid doth seem
To have thee crowned withal.
She concludes by asking herself for husband to home soon so that can convince him to do what is needed to be done- kill King Duncan
so that Macbeth can take his title.