The compelling issues in The Merchant of Venice are the bond between Shylock and Antonio, requiring " a pound of flesh" from Antonio and Portia's need to fulfil her father's wishes in finding a suitor as "the will of a living daughter curb'd by the will of a dead father"(I.ii.20) drives the story forward.
Portia will be the one who measures out the justice and seemingly grants Shylock his bond - "O wise young judge, how I do honor thee" (IV.i.220), only to ensure that he cannot collect on his bond as he cannot take his (literal) pound of flesh without spilling blood which would contravene "the laws of Venice."(306)
Shakespeare attempts to show that the law will prevail but will be measured against compassion and the need to do the right thing. Portia is merciful but also mindful that the laws, very relevant to the audience of the day, must be obeyed. She reminds Shylock how "It blesseth him that gives, and him that takes" (189)but his interest is only in the upholding of the law as he wonders why he should show mercy "On what compulsion must I?"(178)
Portia's handling allows the audience to almost gloat as there will have been no sympathy for "the Jew" in Shakespeare's day. Portia has pledged her love for Bassanio and honors him by doing everything she can (within the confines of the law) to save Antonio as she knows how important he is to Bassanio who "would lose all....to deliver you."(281)
By bringing everything together at this point, Shakespeare has intensified the play. Shylock is unforgiving as he "crave(s) the law"(201). Portia is the epitome of mercy as "mercy seasons justice"(191). Bassanio is desperate to save his friend whom he holds dear above "all the world"(279) and Antonio is prepared to make the ultimate sacrifice for his friend as "I am fall'n to this for you."(260) Bassanio and Portia love each other, Antonio loves his friend and Shylock loves the law.