It blesseth him that gives and him that takes:
Tis mightiest in the mightiest; it becomes
The throned monarch better than his crown:
His sceptre shows the force of temporal power,
The attribute to awe and majesty,
Wherein doth sit the dread and fear of kings;
But mercy is above this sceptred sway;
It is enthroned in the hearts of kings,
It is an attribute to God himself;
And earthly power doth then show likest God's
When mercy seasons justice. Therefore, Jew,
Though justice be thy plea, consider this,
That, in the course of justice, none of us
Should see salvation: we do pray for mercy;
And that same prayer doth teach us all to render
The deeds of mercy. I have spoke thus much
To mitigate the justice of thy plea;
Note that this is the third line in which Portia has used the word “justice.” Similar to Marc Antony’s continued use of the word “honorable” in his  Funeral Oration , the repetition is intended to make the reader consider how the word relates to the scene. 
 Here, Portia tells Shylock to ask for mercy, which is an attribute of God, rather than ask for justice. 
 Portia essentially argues that if God were to judge us all with complete objectivity, we would all end up in Hell because we have all done wrong to a greater or lesser degree.  Instead, she argues, we pray for God to show us mercy in spite of our fallen nature and the sins we’ve committed – and by extension, she argues, the fact that we pray for God to show us mercy should teach us to render mercy to other people when they beg of it from us.  It’s the ultimate “Do unto others as you would have them do unto you” argument – and it is fundamentally at odds with Shylock’s notion of a strict and condign justice which makes no room for mercy. 
 However, it absolutely has to be noted, and more than once, that Portia – a rich insider safe behind the multiple protections of wealth and class – is asking a person who has been utterly marginalized in this society to show mercy to someone who has persecuted him repeatedly.  The “turn the other cheek” argument that Portia is presenting here is at cultural odds with the “eye for an eye” justice Shylock demands – and on what moral basis does Portia ask this?  What right does Portia, or the Venetian society she represents, have to demand that Shylock show mercy when none has been shown to him, and when there is little practical value in his doing so?  Are we, the audience, to imagine that if Shylock takes the first step, acts the bigger man, etc., and shows Antonio some mercy here that the Venetian society in which he lives will turn around and say, “You know, we need to start treating the Jews in our community with fairness and equity”?
The Quality of Mercy