Discuss the rivalary between Antonio and Shylock and what were the consequences?

Act I, scene iii offers background on the problems between Antonio and Shylock.
Antonio hates Shylock because he is a Jew and moneylender, and sometimes says and does nasty things to him. Antonio will call him a:

misbeliever, cut-throat, dog / And spit upon Jewish gaberdine

In this period, the Roman Catholic Church banned charging interest on loans believing that doing so took unfair advantage of people in need. Judaism, however, did not prohibit charging interest, and since Jews were subjected to discrimination and persecution, which made it impossible for them to pursue many of the higher-status professions, they would often become moneylenders.
While  Antonio verbally attacks Shylock for lending money, Shylock, not surprisingly, hates Antonio for insulting and shaming him. He also hates it when Christians lend money without charging interest, as this threatens his own business.
Unfortunately for Antonio, he ends up needing a loan for his friend, and has already bitten the hand that will feed him (Shylock's). Shylock wants revenge. In consequence, he offers Antonio an interest free loan but demands that if Antonio can't repay the loan, he forfeit a pound of his flesh, to be cut off any part of Antonio's body that Shylock chooses. Antonio agrees, and then his ships sink so that he can't sell the cargo and repay the loan. Shylock demands his pound of flesh. Since he can demand that Antonio's heart be cut out to repay the loan, this becomes a death sentence. At this point, the play reaches a crisis point.