Lending money on fractional reserves at an interest rate that should cover defaults did not exist until relatively recently in the western world. It was classified as usury and banned by the Catholic Church the same was that the Islamic world does currently.

>I fail to see how that should have brought significant change (rather than a bit of convenience).

A bit of convenience can create massive change. What's the difference from online banking compared to buying at a store other than a bit of convenience? You can do all the same things in person, yet we've seen massive changes in logistics and ourchasing habits because of it. Checks that people _trusted_ were massive. You could write someone a document that let them go to somewhere nearby to get gold, rather than carrying it on the roads. This was the modern era where you can travel most European or american roads safely. The world wasn't lawless but the law didn't extend much farther out than the local rulers could patrol. There was always the risk of bandits taking your shipments on land or pirates on the sea. By having a banking system the risk of transferring currency dropped massively and that would lead people to engaging in enterprises that were too risky previously