After his close friend Bassanio comes to Antonio to borrow money so that he can be a suitor to win Portia, rather than let his best friend lose his dearest hopes, Antonio, whose finances are all invested in his three merchant ships, borrows 3,000 ducats from Shylock. The terms of this loan allow Shylock to extract a pound of flesh from Antonio if he does not repay the loan on time. While Antonio certainly gambles that his ships will return in sufficient time for him to repay Shylock with his profits, he does take risks because storms at sea could rather easily destroy the ships of the time that have gone on such long voyages.
While this impulsive act of Antonio's to give so freely to his friend--"My purse, my person.../Lie all unlocked to your occasions"(1.1)-- is certainly in contradiction to his personality as a shrewd merchant and lender, there are critics who speculate that Shakespeare creates Antonio to be Christ-like in his unselfishness; moreover, Elizabethan audiences would be anti-Semitic, and against Shylock's charging of interest. Christians like Antonio did not charge interest as exhorted in the Bible:
Deuteronomy 23:19-23: "You shall not lend upon interest to your brother.... To a foreigner, you may lend upon interest, but to your brother, you shall not lend upon interest.
So, when he demands his payment, Shylock displays his spite and immoral character, thus underscoring contemporary and Christian beliefs, even though he justifies his charging of interest with another passage from the Bible [Genesis: 30,31].