I am teaching a Sunday School class on "Happiness and Faith." Reviewing the research on this subject, I have come to this partial insight.
Happiness comes more from the process of doing something worthwhile with other people we care about than it does from any specific outcome of that process. This is a common finding of happiness research.
Religious people are, on the whole, happier, than non-religious people. This is also a standard finding of happiness research.
Happiness correlates more with religious belonging than with believing - that is, people who are active in religious communities report higher happiness, whereas people with strong religious beliefs who are not part of religious communities do not report higher levels of happiness.
I believe what religious institutions do that adds to happiness is to give structure and permanence to the process of doing good things together with other people. One-off group projects are good, and an interest in civic betterment can produce such projects. But for sheer persistence and long-term effect, nothing can compete with religious institutions for getting a group of people to work together for the common good week after week, year after year, decade after decade.