Their understanding of manhood allows the political order depicted in the play to descend into chaos.
At the same time, however, the audience cannot help noticing that women are also sources of violence and evil.
One of Shakespeare’s most forcefully drawn female characters, she spurs her husband mercilessly to kill Duncan and urges him to be strong in the murder’s aftermath, but she is eventually driven to distraction by the effect of Macbeth’s repeated bloodshed on her conscience.
In each case, ambition—helped, of course, by the malign prophecies of the witches—is what drives the couple to ever more terrible atrocities.
While the male characters are just as violent and prone to evil as the women, the aggression of the female characters is more striking because it goes against prevailing expectations of how women ought to behave.
Lady Macbeth’s behavior certainly shows that women can be as ambitious and cruel as men.
In the same manner that Lady Macbeth goads her husband on to murder, Macbeth provokes the murderers he hires to kill Banquo by questioning their manhood.
Such acts show that both Macbeth and Lady Macbeth equate masculinity with naked aggression, and whenever they converse about manhood, violence soon follows.
This is proven several times throughout the course of the play; through Lady's Macbeth provoking Macbeth to kill by doubting his manhood, through Macbeth questioning the manhood of the hired murderers in order to convince them to kill Banquo, and through Malcolm telling Macduff to seek revenge in a manly fashion after his family has been murdered.
The main theme of Macbeth—the destruction wrought when ambition goes unchecked by moral constraints—finds its most powerful expression in the play’s two main characters.