Shylock, although he is a major influence in the story, only appears in five scenes.
The most revealing of his feelings for Antonio are in Act I, scene 3. He tells us that he hates Antonio because he is a Christian and that he hates "our sacred nation".
Later in the scene, he talks about all the abuse he has suffered at Antonio's hand and Antonio makes no bones about his hatred of Shylock. It would seem that the feeling is mutual.
The pound of flesh is made in a merry jest but when Shylock has a chance to get his revenge against his enemy, he doesn't hesitate.
Business is one thing but this is also personal. The hatred is mutual.
you see that the christianity and jews were the foe of each other and that was in the mind of shylock too.One more thing that Antonio had done with him wrong also.He had called him dog ,you know he spat upon him,he alway try to show that he is major.So i think these were the causes that turns to Shylock in cruel fellow.
The answer posted January 9, "The hatred is mutual," might help one to understand why Portia's "The quality of mercy" speech is regarded as the keynote, so to speak, in the play. One might also note that each of three occurrences of the word "hate" in Shylock's speech is linked to passages in ROMEO AND JULIET. The first, "I hate........but more," is linked to Romeo's "Here's much to do with hate, but more with love"(ROM1.1). The second, "But yet I'll go in hate"(MV2.5), is linked to Act 1, scene 4 in ROMEO as both Romeo and Shylock express misgivings about going to the respective social gatherings. The third, Shylock's "lodged hate"(4.1), is linked to to Romeo's "As if that name" speech(ROM3.3). Therefore yet another love triangle, Shylock, Leah and Antonio is suggested.