I ran intoa relevant paper on the ‘economics of religion’ which offers some interesting theories:
As one example of the approach, consider Ekelund et al.’s treatment of the church’s usury doctrine (analyzed more formally in Ekelund, Robert Hébert, and Tollison 1989). Here rent seeking is seen as the primary motivation for the maintenance of a particular doctrine. The central church’s monopoly position allowed it to extract rents from downstream producers (the clergy) and from input suppliers (banks) by controlling the borrowing and lending interest rates. The authors argue that usury rules enabled the church to borrow at low rates while lending (through papal bankers) at much higher rates, and they cite many sources spanning several centuries to defend their claims.
One can, however, tell a very different, though perhaps not mutually exclusive, story. Carr and Landa (1983, p. 153) and Edward Glaeser and José Scheinkman (forthcoming) argue that usury laws acted as a form of social insurance against shocks that were not otherwise insurable. In all societies, but especially simple agrarian ones, individuals face the constant threat of bad harvests and other unpredictable disasters. Interest rate restrictions can benefit the victims of bad shocks (who will have high demand for credit) while penalizing those who had experienced good shocks (and are thus in a position to lend). Glaeser and Scheinkman formalize this model and derive a variety of nonobvious predictions, including some that they test using American data. The model’s greatest appeal lies in its ability to account for the pervasive nature of interest restrictions, which arise in societies and religious traditions far removed from those of medieval Europe.
I ran into a relevant paper on the ‘economics of religion’ which offers some interesting theories: