From an article in The Economist:

Jonathan Gruber, an economist at the Massachusetts Institute of Technology, claims that regular religious participation leads to better education, higher income and a lower chance of divorce. His results* (based on data covering non-Hispanic white Americans of several Christian denominations, other faiths and none) imply that doubling church attendance raises someone's income by almost 10%. So how might churchgoing make you richer? Mr Gruber offers several possibilities. One plausible idea is that going to church yields "social capital", a web of relationships that fosters trust. Economists think such ties can be valuable, because they make business dealings smoother and transactions cheaper. Churchgoing may simply be an efficient way of creating them. Another possibility is that a church's members enjoy mutual emotional and (maybe) financial insurance. That allows them to recover more quickly from setbacks, such as the loss of a job, than they would without the support of fellow parishioners. Or perhaps religion and wealth are linked through education. Mr Gruber's results suggest that higher church attendance leads to more years at school and less chance of dropping out of college. A vibrant church might also boost the number of religious schools, which in turn could raise academic achievement. Finally, religious faith itself might be the channel through which churchgoers become richer. Perhaps, Mr Gruber muses, the faithful may be "less stressed out" about life's daily travails and thus better equipped for success. This may make religion more appealing to some of those who turn up only once a year. But given that Jesus warned his followers against storing up treasures on earth, you might think that this wasn't the motivation for going to church that he had in mind.