I recall reading that CS Lewis was deeply troubled by the casual acceptance of usury, but I remember feeling baffled at the time since borrowing is now so ubiquitous and it never occurred to me that it had been otherwise. As I got older and read more, I came across the trope of the Jewish money lender in historical literature (Shakespeare's Shylock is probably the most famous). At any rate, I realized that the Christians were borrowing money from the Jewish guy since it wasn't considered acceptable for Christians to lend money. Lending, as recently as the early 19th century, was as abnormal for Christians to engage in then as it is normal today. Clearly there are plenty of Christians in banking today, and the western economy is largely based on borrowing and lending at interest. At some point the paradigm shifted. So, I'm curious, when did the Christian attitudes about lending change? How did it go from being an awful sin for Christians to a normal 9 to 5 job. Was there a major historical event that ushered in the change?
You might be interested in this earlier answer of mine, which asks about the economic impact of expelling Jews from cities and countries in the late Middle Ages was, if they were the only ones allowed to lend money at interest.
The answer is basically: "when it was necessary, people found or theologized a way."
This thread, about how medieval Jewish moneylenders could enforce their debts, might also be of interest.