In Macbeth, the theme "loss of innocence" is relevant. Although Macbeth is a mighty warrior, the thought of murdering King Duncan causes him to shiver as his hair stands on end:
This supernatural meeting
Can’t be bad, only it can’t be good either. If it’s bad,
Why has it given me promise of success,
That began with a truth? I am Baron of Cawdor.
If it’s good, why do I give in to that suggestion
Whose horrid image makes my hair stand on end,
And makes my heart pound so hard they knock at my ribs,
Against my will to stay calm? My current fears
Are less than horrible imaginings.
My thought, whose murder is still only a fantastic idea,
So shakes my manhood, that functioning like a man
Is smothered in unfounded allegations; and nothing is
Only what is not.
Here, Macbeth is contemplating killing King Duncan and it causes his heart to pound. It shakes his manhood and causes his manhood to fail him. Clearly, Macbeth is innocent of such horrible imaginings. He cannot even contemplate murder with any sense of confidence. His heart is pounding against his ribs. He admits to current fears. He exclaims that murder is a fantastic idea. He is shaken to the very core at such a thought.
Later, Macbeth proves his innocence when he tells Lady Macbeth that they will proceed no further in the business of murdering King Duncan:
We will proceed no further in this business.
He has recently honored me, and I now have the
Golden opinions from all sorts of people,
Which I want to enjoy for a bit longer, and
Not cast them aside so soon.
Lady Macbeth challenges his manhood, asking him if he is afraid:
Are you afraid
To be the same man in reality
As the one you wish to be? Would you have the crown
Which you believe to be the ornament of life,
And yet live like a coward in your own self-esteem,
To this question, Macbeth loses his innocence and states that he is convinced to follow through with the murdering of King Duncan:
I’m convinced, and I commit
Every part of my body to this terrible event.
Although he is moved with fear in the beginning, he has a loss of innocence; he later murders not only King Duncan but also the guards. Then he proceeds to have his good friend Banquo murdered. Likewise, he has Macduff's family murdered. His loss of innocence is clear. He becomes a cold blooded murderer. He is guilty of murder. Killing becomes easier for Macbeth. The same man who was shaking and shivering while his heart pounded at his ribs loses his innocence and becomes a cold calculating murderer.