Why does Shylock insist on the punishment for forfeiting the bond?

Antonio pleads with Shylock to listen to him, but Shylock says, "I have sworn an oath that I will have my bond," (3.3.4) and refuses to listen to any of the pleas for mercy. After Shylock departs, Antonio tells Solanio that Shylock hates him because he used to loan money to men who were in debt to Shylock, thus preventing Shylock from collecting the forfeiture. Antonio is prepared to pay his "bloody creditor" the next day in court, but prays that Bassanio will arrive in time to watch him die. Shylock wants his bond because, in part, he has been the source of so much ridicule by Christians such as Antonio. While being reviled for being a Jew and lending money for profit, he has been asked for money by the very people who persecute him.  

Shylock insist on punishment for forfeiting the bond since he was desperately waiting for te renenge ans when he hears about Antonio's ship wreck, he couldn't wait. Althought Antonio pleads Shylock to listen to him but stubborn Shylock keeps on repeating, " I have sworn an oath that I will have my bond, " and refuses to listen to Antonio and even tells the jailer to not show mercy on Antonio. Antonio tells Solanio that Shylock hates him because he lend money to those who couldn't pay back to Shylock thus leading to loss for Shylock. Tha main reason for forfeiting the bond is for revenge. Shylock wants to take revenge on Antonio for insulting and discriminating him for being a Jew.