Explain with textual proof the medieval economic system as it changes to capitalism.
At the time that Shakespeare was writing this play, the economic system of Europe was moving toward capitalism and trade. This system pretty much required that money be available to lend.
The lending of money at interest is prohibited in the Bible. This prohibition was increasingly being ignored because of the needs of the new system. But there were still lots of traditionalists who still believed that lending at interest was evil.
In the play, Shylock represents the new economic system. He argues that lending at interest is okay. He criticizes Antonio for not doing so himself.
I hate him for he is a Christian:
But more, for that in low simplicitie
He lends out money gratis, and brings downe
The rate of usance here with us in Venice.
[I. iii. 42-5]
In contrast, Antonio represents the old ways and he criticizes Shylock for lending at interest. He points out, as in the next quote, that he himself does not do this.
I would suggest that you look for other quotes by Shylock and Antonio if you need further textual proofs.