The primary grievance that Antonio has against Shylock is that he is greedy—for charging interest to those who borrow money from him when they are in need. The Venetians implicitly contrast Shylock's greed with the generosity that they show one another. For instance, Antonio is willing to place his whole "purse and person" at Bassanio's disposal and regularly saves other Christians from having to pay interest to Shylock by paying off their debts for them.
It seems that, like love or mercy, generosity is limitless, unbounded. However, The Merchant of Venice also frequently begs the question of whether friends aren't using friends, or lovers their lovers, for materialistic reasons. For instance, why is the perpetually indebted Bassanio so intent on wooing the rich Portia? And as Portia's and Nerissa's anger over the rings that their husbands give away in the final scene reflects, even the freest gift-giving comes with strings attached, like the rules governing Shylock's more frankly capitalistic contracts.
Greed vs. Generosity ThemeTracker
Greed vs. Generosity Quotes in The Merchant of Venice
I shot his fellow of the selfsame flight
The selfsame way, with more advised watch,
To find the other forth; and by adventuring both,
I oft found both.