Discuss the role of motivation for the characters of Macbeth, Lady Macbeth, and the Three Witches.

Macbeth is chiefly motivated by his unchecked political ambition. He desires to take the throne despite knowing that such ambition is devious and destructive. Although he, at times, hesitates to follow through with the plan of murdering Duncan, his "black and deep desires" prove to be too powerful to be ignored. With the help of Lady Macbeth, who verbally manipulates her husband, he summons enough courage and murders the innocent king:

Hear it not, Duncan;...

Macbeth is chiefly motivated by his unchecked political ambition. He desires to take the throne despite knowing that such ambition is devious and destructive. Although he, at times, hesitates to follow through with the plan of murdering Duncan, his "black and deep desires" prove to be too powerful to be ignored. With the help of Lady Macbeth, who verbally manipulates her husband, he summons enough courage and murders the innocent king:

Hear it not, Duncan; for it is a knell
That summons thee to heaven or to hell.

Lady Macbeth is primarily motivated by her lust for power and control. At the beginning of the play, she is a very evil and manipulative woman, who challenges her husband's courage and masculinity in order to solidify his ambition of killing the king. She appears to be more villainous than her husband at the beginning of the play. When her husband falters for a moment, she urges him to pursue his ambition and motivates him to take the throne. All of this reflects badly on her when she becomes plagued by guilt towards the end of the play.

As far as the witches are concerned, one of their roles is to show what characters would display the propensity for evil. The witches motivate Macbeth because they sense he is capable of embracing evil. They sense he is corrupt, so they encourage him to follow his ambition, so they can take pleasure in seeing his imminent demise. Here is what Hecate, the chief witch, thinks about Macbeth:

A wayward son,
Spiteful and wrathful, who, as others do,
Loves for his own ends, not for you.

Unlike Macbeth, Banquo is not seduced by the witches. He refuses to be obsessed with their prophecy, as opposed to Macbeth, who seeks out the witches later in the play because he has become so dependent on them.