The Duke pleads Shylock to be "touched with humane gentleness and love" by "glancing an eye of pity on [Antonio's] losses" while simultaneously referring to him as barbaric as "stubborn Turks and Tartars never trained". The word "gentleness" connotes Christianity and it's paired with the word "love" because he equates Christianity with love. However, Shylock is not a Christian and he does not pity Antonio because did break his bond and failed to repay three thousand ducats in time. The word "gentle" is also repeated when the Duke tells Shylock "We all expect a gentle answer, Jew". (4.1.26-35) Once again, he expects Shylock to show Christian behavior while at the same time calling him a Jew.
Even Antonio, who should be the one begging for Shylock's mercy, describes Shylock's "Jewish heart" as unchangeable and as hard as stone: "You may as well do anything most hard/As seek to soften that than which what's harder?--/His Jewish heart" (4.1.49) If his Jewish heart is hard, then Christian hearts must be the same because they never seem to show any compassion whatsoever to evoke empathy from Shylock.
Gratiano interprets Shylocks determination to uphold justice as a "desire": "for thy desires/Are wolfish, bloody, starved, and ravenous." (4.1.139-140) I think it's true that Shylock's vengeance does make him deserving of being called as a ravenous, bloodthirsty wolf but in this quote it seems like Gratiano is attributing justice as a bloodthirsty desire instead of a rational societal belief. Justice is usually associated with reasoning and upholding equality, but in the Christian's view mercy overcomes justice.
Portia who is disguised as Balthazar depicts that mercy is not something that is restrained, but rather falling like rain from heaven. "The quality of mercy is not strained/It droppeth as the gentle rain from heaven" (4.1.190-191) She describes mercy as being "gentle" which also emphasizes mercy as being a Christian value. The repetition of the word "gentle" undoubtedly conveys the Christian mindset of how mercy is above all things, even justice. Thus not expressing mercy would be considered as a wrongdoing in the Christian view.
What particularly interested me was how Portia undermined justice by saying that justice does not give salvation, only mercy will.. "Therefore, Jew,/Though justice by thy plea, consider this:/That in the course of justice none of us/Should see salvation. We do pray for mercy" (4.1.203-206) Portia used the word "us" which made it seem like it included Shylock in Christian salvation when they clearly point out how Shylock is a Jew. Maybe it served to prepare for Shylock's conversion to Christianity....perhaps that's why there were multiple uses of the word "gentle".
In the end, Shylock was forced be for mercy himself, indicating that mercy was the only solution to injustice: "Down, therefore, and beg mercy of the Duke.' (4.1.378) At the end of the Act 4.1, it was also interesting how Portia requested for Antonio's ring when Bassanio insisted that he should repay her. Portia referred to the process as begging, which I think draws connection with the act of begging for mercy. In between the Christians, begging involved objects and monetary value whereas in with Shylock's trial it involved begging for mercy. I wonder if this is significant to the Christian hypocrisy or maybe I'm just reading a little too deep into it.
"I see, sir, you are liberal in offers/You taught me first to beg, and now methinks/You teach me how a beggar should be answered." (4.1.456-458)