Each of the three women characters in Shakespeare's The Merchant of Venice demonstrates the strength of character and the indomitable spirit that enables them to overcome the limitations imposed on them by the male-dominated, 16th-century societies of Italy (where the play is set) and England (where the play was written).
Portia is a wealthy, beautiful, intelligent heiress who lives in the idyllic hilltop town of Belmont, located not far from Venice.
Nerissa is Portia's "waiting woman" or lady-in-waiting, which is to say that Nerissa is Portia's personal assistant, companion, counselor, confidant, and, when necessary, Portia's "partner-in-crime."
Jessica is the money-lender Shylock's daughter and only child.
Portia no doubt realized her own worth from an early age. Her life is one of wealth and privilege, and aside from being a woman, she's been taken seriously throughout her life because of her elevated status in society.
Nerissa, not afraid to speak truth to power, takes Portia to task, however, for taking herself and her privileged status a little too seriously.
The first time the audience sees Portia, in act 1, scene 2, she's complaining about the way life is treating her.
PORTIA. By my troth, Nerissa, my little body is a-weary of this great world.
NERISSA.You would be, sweet madam, if your miseries were in the same abundance as your good fortunes are; and yet, for aught I see, they are as sick that surfeit with too much, as they that starve with nothing. (1.2.1–6)
Since her father's death, Portia has managed the estate he left to her quite well on her own. She's well-regarded in the community and highly sought after by many—if vacuous and insufferable—suitors, who seek her hand in marriage and who are willing to submit to her father's strict requirements in order to obtain that hand.
Jessica, long dominated by her father and subject to his strict, if not oppressive upbringing, has only recently discovered her self-worth. She is determined to separate herself from Shylock and live her own life.
JESSICA. Alack, what heinous sin is it in me,
To be asham'd to be my father's child!
But though I am a daughter to his blood,
I am not to his manners: O Lorenzo!
If thou keep promise, I shall end this strife;
Become a Christian, and thy loving wife. (2.3.16–21)
Although Jessica elicits compassion from the audience for Shylock's treatment of her, she also elicits a certain level of antipathy for her treatment of him. When she elopes with penniless Lorenzo, she not only betrays Shylock and demonizes his religion, but she also steals Shylock's money and a turquoise ring given to him by Jessica's late mother.
Portia remains loyal to her father by honoring his wishes and submitting to the conditions he imposed on her with regard to her marriage, but Portia, too, is not without her own faults. She exhibits a deep-seated racial bigotry. Her remarks about the Prince of Morocco, one of her suitors, are clearly racially motivated.
PORTIA. ... [I]f he have the condition of a saint and the
complexion of a devil, I had rather he should shrive me [hear her confession]
than wive me. (1.2.115–117)
When the Prince later chooses the wrong casket, Portia is happy to see his hopes of marriage to her go unfulfilled.
PORTIA. A gentle riddance:—Draw the curtains, go;—
Let all of his complexion choose me so. (2.7.79–80)
There is also the matter of having once declared "The quality of mercy is not strain'd" (4.1.87) and demanding that Shylock show mercy towards Antonio, Portia leads the court in humiliating the vanquished Shylock—destroying his livelihood, ruining him financially, and forcing him to accept Christianity.
The way to be taken seriously in a male-dominated society is to be a man, or pretend to be a man, which is what Portia, Jessica, and Nerissa do. Portia disguises herself as a lawyer and Nerissa disguises herself as Portia's law clerk to effect justice for Antonio. Jessica disguises herself as a page to escape Shylock's parental tyranny.
The racial bigotry that Portia expresses is the same racial bigotry a man might express, and the punishments that Portia imposes on Shylock are the same vengeful retributions that a man might impose on him—particularly a man in Italy or England in the late 16th century.
Speaking about Christians's treatment of Jews, Shylock remarked, "The villainy you teach me I will execute; and it shall go hard but I will better the instruction" (3.1.62–64), meaning that he will treat the Christian characters even worse than they treated him. Portia demonstrates this same attitude about men's treatment of women, and her cruelty towards Shylock reflects the discrimination she faces as a woman. In fact, she "betters the instruction" by treating Shylock worse than she herself has been treated by men. In this way, Portia certainly betters the instruction, but whether she bettered her character is less certain.