W.h. Auden said this quote

After Portia has trapped Shylock through his own insistence upon the letter of the law of Contract, she produces another law by which any alien who conspires against the life of a Venetian citizen forfeits his goods and places his life at the Doge’s mercy. […] Shakespeare, it seems to me, was willing to introduce what is an absurd implausibility for the sake of an effect which he could not secure without it: at the last moment when, through his conduct, Shylock has destroyed any sympathy we may have felt for him earlier, we are reminded that, irrespective of his personal character, his status is one of inferiority. A Jew is not regarded, even in law, as a brother.