If religious doctrines were believed to be true, then it would be very much in the interest of self-interested persons to read the doctrines and apply them to daily life. If, for instance, those who did not adhere to the faith of Islam had to spend an eternity in Hell, even the most philosophically disinclined individual would have a vested interested in believing Islam. If “Give and ye shall receive” (Luke 6-38) were believed to be an accurate claim, then India’s money-obsessed youth would be falling over each other to give money to others. The “Kingdom of Heaven” is enticing for the materialistic, yet how many people strive to be poor in spirit in order to be eligible for that kingdom? (Matthew 5:3) . The Bhagvad Gita’s most famous piece is as clear as it gets — yet few are convinced by this deep metaphysical claim. People do want to be happy and avoid suffering. The Buddha claimed that “desire is the root of all suffering” ( http://www.sacred-texts.com/bud/btg/btg46.htm ) and offered an eight-fold path — if people believed that the Buddha was spot on in his diagnosis and prescription, they’d follow his approach, or at least try hard.

Moving from the general philosophical claims to the more concrete and down-to-earth, many religions offer detailed instruction on mundane topics such as the rules for selling slaves, conducting trade, bequeathing money for after one’s death, etc. This is very concrete instruction, much of it tied to material rewards both in the here and now and in the afterlife. Self-interested individuals who believed in the accuracy of these claims would have a vested interest in following the rules.