In Shylock's recognition of Antonio's hypocrisy, we see that Shylock has an eye for spotting contradiction.
These men are merchants, not theologians engaging in religious debate. Nevertheless, in what would otherwise be a neutral market of barter and exchange, where the highest bidder would simply acquire the desired item, we find economic decisions hinging upon religion and race. The market is tainted by racism. Shylock draws attention to this by pointing out Antonio's contradictory behavior. By borrowing from Shylock, Antonio enters into a contract with a man he has publicly abused: "many a time and oft / In the Rialto you [,Antonio,] have rated me / About my moneys and my usances. . . You call me misbeliever, cutthroat dog, / And spet upon my Jewish Gaberdine, / And all for use of that which is mine own" (1.3.116-123).
Shylock's ability to spot this contradiction indicates that he is a socially aware merchant who wants to draw attention to the injustice that inhabits the Venetian market.