I hear by declare that no Cristian should be involved in the act of usury!
I'm sorry sir, I lost the money and I have a different currency than you.
You must pay me my money back!
I am Giovanni Medici and I have created banks! So come everyone to see this amazing idea.
The catholic church proclaimed that no Christian must be allowed to participate in the act of usury. They thought is was against God's law so many of the catholics left the church because they could go borrow money. The church also made a rule that the Jews must not borrow from their brother, other Jews, but they can lent money to Christians. They were also excluded from the community and had to live in ghettos because they were not Christians.
A lot of times people wouldn't be able to give their money back because they had to pay it to someone else or they lost it. Another issue with trading and exchanging was that everyone lived in different city-states and so they had different currencies. This would cause problems and people would have many debuts to pay and they wouldn't have their own currency.
A man named Giovanni Medici came up with the idea of banks because eh wanted a place that could hold all of the different currencies and a place where you can exchange your money for a different kind if you are a merchant or a trader with people across the seas. This was much easier for everyone and everyone was happy about this idea.