According to the evidence presented in the play, Shylock's hatred toward Antonio is based on the fact that Antonio is a Christian who treats him poorly and lends money without charging people interest. In Act One, Scene 3, Bassanio assures Shylock that Antonio will pay back his loan of three thousand ducats. When Antonio enters the scene, Shylock says to himself,
"I hate him for he is a Christian,
But more for that in low simplicity
He lends out money gratis and brings down
The rate of usance here with us in Venice.
If I can catch him once upon the hip,
I will feed fat the ancient grudge I bear him.
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