Usury

Usury is a sin because, in a zero growth economy, people with money to lend would end up owning everything in the space of two or three generations. Traditional cultures are all based on an idea of zero growth. Agriculture is the source of essentially all wealth, and this has a constant output in these societies. There might be good years and bad years, but overall harvests move up and down around the average, so wealth remains constant. Merchants, (the people with money that could be lent), are almost always regarded as the lowest people in the society, only one step above peasants. To a traditional society, they would be the most disruptive class of all, for they will always be trying to increase their wealth, and, in a zero growth society, this will always come at the expense of some other group. The idea that merchants could be the dominant group in society appeared as Europe expanded out into the rest of the world, and actual growth became possible, even if only at the expense of other societies. At this point earning money by lending money was no longer a certain way to ruin, and a threat to social order; it was a way to make expansion even faster.