Northrup Frye writes in his essay "The Argument of Comedy":
In the last scene, when the dramatist usually tries to get all his characters on the stage at once, the audience witnesses the birth of a renewed sense of social integration.
In The Merchant of Venice, the last scene takes place in Belmont as the lovers gather in this enchanted place. This is a joyful, playful, festive gathering. Notably absent, however, is Shylock. He is the antagonist who has attempted to thwart the joy of the lovers. Frye describes such antagonists as follows:
These are always people who are in some kind of mental bondage, who are helplessly driven by ruling passions, neurotic compulsions, social rituals, and selfishness.
Shylock is driven by the tragic flaw of wanting revenge on Antonio at all costs and has paid the price. It is as if the social integration Frye speaks of can't be achieved unless Shylock, whose presence has loomed in an ominous way over the lovers throughout the play, is expelled. Love and revenge do not mix—except that the women do exact a certain amount of playful, yet painful, revenge on their lovers for giving up their rings. The lovers may want to expel a vice but perhaps don't fully recognize it exists as well in their own hearts, even if in a light-hearted way.
Antonio is another character who appears on the fringes in Belmont at the end. He is more spectator than participant. He has done all he can to bring together the marriage of Portia and Bassanio, but now his participation in his beloved friend's life must diminish. Nevertheless, he inserts himself into the upcoming marriage by pledging his "soul" as collateral to convince Portia of Bassanio's faithfulness, just as he once pledged his body for Bassanio. Yet this is sadly unnecessary: Portia is already convinced of her beloved's faithfulness and simply teasing him. Although Antonio participates in the overall festive joy as the news comes that his ships have arrived safely to port, money seems a dim second to the joy of relationship.
Both Shylock and Antonio have been important for driving the difficulties that interfere in making true love run "smooth," to borrow a phrase from A Midsummer Night's Dream. Yet these difficulties have helped the lovers to bond all the more closely.