Portia addressed herself to Shylock as a lawyer and pleaded for him to have mercy on the accused. She was giving him one last chance to show mercy. This way, the audience could not feel sympathy for the Jew when his punishment incurred. We must remember that this is a comedy after all. Of course, she has no effect on Shylock and he demands his pound of flesh. He reiterates the initial bond and he wants his revenge. Of course, this does not happen in the end since he is allowed his pound of flesh, but no blood.
Portia appears as a lawyer in the court and addresses herself to Shylock advocating the case of Antonio. She tries to impress upon Shylock the significance of mercy. She says that mercy is an essential trait of human beings. It is spontaneous and justice should be tempered with mercy. But all her efforts and persuasive words fall flat on Shylock as he was adamant on wreaking vengeance on Antonio. Finally, Portia asks Shylock to have a pound of flesh from the chest Antonio as per agreement of loan taken by Antonio but with the condition that not even a single drop of blood should flow from Antonio's body. Since The Merchant Of Venice is a comedy, Portia's speech and the condition mentioned therein jibes well with the play causing deep disappointment in the Jew known for extracting exorbitant rate of interest on the loans given and thriving thereon.