According to social contract theories of morality, right and wrong are nothing more than the agreement among rationally self-interested individuals to give up the unhindered pursuit of their own desires for the security of living in peace. I argue that theism provides a better motivation for rationally self-interested persons to be moral. In the context of our moral development, we are involved in the project of becoming certain kinds of persons, and this project must extend into the next life within a community similar to Kants kingdom of ends. The temporary squelching of desire necessary for the common good is rewarded in the long run with long-term desire-satisfaction (including both self-interested and altruistic desires), but the squelching of desire makes sense only, I argue, if the moral project continues into the next life.
Kelly James Clark, "Why Be Moral? Social Contract Theory Versus Kantian-Christian Morality," Journal of Markets & Morality 6, no. 1 (Spring 2003): 81-98