Portia is not only wealthy and beautiful, she has a razor -sharp wit, which tells the audience at the very outset that she is not meant for a merely decorative role. Though Bassnio only as "In Belmont is a lady richly left,/And she is fair and, fairer than that word,/ Of wondrous virtues, (I,1) we see her ready wit and her scorn for lack of learning when she comments on her various suitors, Falconbridge for instance, remarking: "He is a proper man's picture, but alas, who can converse with a dumb-show".
This shows that not only is she herself intelligent, she is also looking for a savvy life partner, who could meaningfully engage her in proper conversation. Her sarcastic remarks about her suitors and others stem from her confidence in herself, she is secure in the knowledge of her own superiority. This confidence usually marks the hero of a story or play, and overtaking Bassanio and Antonio in shrewdness, wisdom and initiative, Portia almost becomes the hero of the play.
Once she hears of Antonio's plight, she is brisk and matter-of-fact and knows exactly what is to be done, and in what order: "First go with me to church and call me wife, And then away to Venice to your friend; For never shall you lie by Portia's side With an unquiet soul. You shall have gold To pay the petty debt twenty times over"(III, 2). She is more like an action-hero in her manner, than a delicately feminine heroine. She decides to go to Antonio's aid of her own volition, not only showing initiative, but also a large heart, another requirement for the character of a hero.
Her supreme confidence never leaves her as she dresses the part of a man, and she knows she will be taken at a face value despite her constructed masculinity: "...they shall think we are accomplished/ With that we lack". Once in male garb, Portia comes into her own, because people take her more seriously in this guise than they had when she appeared in her true nature as a woman. She is heroic indeed in stepping into the court at Venice, posing as a learned lawyer, in front of the Duke and her husband in the guise of a man, risking discovery and its possible attendant consequences.
In a patriarchal set up, Portia goes against the norm by pretending to be a man; and the fact that she is able to pass of as a learned lawyer goes to show that the accepted limitations on a Renaissance woman were not all necessarily true. Given the right kind of education and opportunity a woman like Portia could well become the main protagonist. A hero is an example to all, and Portia makes a worthy example for all the women of her age.
Not only does she step in, she is able to argue the case very well indeed, and Shakespeare gives her importance by giving her one of the best-known speeches of all his body of work. She appeals to Shylock to be more considerate: "The quality of mercy is not strained./ It dropeth as the gentle rain from heaven/ Upon the place beneath. It is twice blest:/It blesseth him that gives and him that takes.'Tis mightiest in the mightiest; it becomes/ The throned monarch better than his crown".
But then she comes up with the clause of not shedding blood while carving out the pound of flesh. And here, she does not show the sort of mercy to Shylock that she had begged