Lady Macbeth is one of literature's most discussed characters. Contrary to many of the female characters created by Shakespeare's contemporaries, Lady Macbeth is strong and power hungry, willing to manipulate her husband to make sure that the crown of Scotland sits upon his head. She schools him on how to behave in a manly fashion and even invokes the dark spiritual forces to "unsex" her and take away any womanly inclination she might have that could cause her to behave in a vulnerable or feminine way. Lady Macbeth, by the play's end is broken and deranged. Her role in "Macbeth" seems to be to warn women of the desperate fate that awaits them if they try to "escape" their natural femaleness and usurp a masculine sense of power.
It is safe to call Lady Macduff the dramatic "foil" of Lady Macbeth, since her behavior is the exact opposite of Macbeth's wife. Lady Macduff's husband flees Scotland in fear of his life, but leaves her behind. She does criticize her husband's actions, but dutifully holds her ground at their family home, where she and her son are murdered by Macbeth's henchmen. She personifies all the "feminine" qualities that Lady Macbeth lacks: motherly love, steadfast devotion and passive acceptance.
Shakespeare names the characters "The Weird Sisters," but these three characters are commonly referred to as the witches. There was, throughout Europe a fascination with, and repulsion of, witches during Shakespeare's day. Women throughout Europe were being accused and convicted of performing witchcraft. Those who were convicted were killed for their crimes. Shakespeare's audience, for the most part, would have completely believed in, and may have been terrified of, the witches in "Macbeth." Their presence definitely adds to the scary creepiness of the play's atmosphere. It is interesting to note that these witch hunts, for the most part, targeted only women and many have denounced the actions of those who persecuted "witches" as attempting to punish women who were seen by the community as too independent or "weird."
The role of women in any of Shakespeare's plays, including "Macbeth," must include a bit about the actors of Shakespeare's theater. There were no women performers. Young boys and young adult men played these roles, so it is often observed that Shakespeare, being a man of the theater, took advantage of the obvious "real" sex of the actor playing Lady Macbeth when he opted to write her as such a "masculine" character. The weird sisters also might have been presented as somewhat androgynous in appearance, probably sporting some sort of facial hair. This fuzziness around the gender of these magical characters would have added to their other-worldliness.