Believers are usually driven to share their truths with others. This is particularly true for monotheistic believers. The conviction that there is only one true deity in the universe heightens the sense of responsibility to share this unique truth with others. There is almost a moral imperative associated with this sharing. Given the conviction of truth, by what right can the believer withhold that blessing from fellow-humans? To be sure, there is a second and less altruistic side to the commitment to sharing truth, and that involves the doubt and uncertainty associated with religious belief. One of the simplest techniques for dealing with doubt and uncertainty is to enhance the number of fellow-believers. Indeed, the very process of addressing others with supposedly certain truth augments for those doing the outreach the conviction of the veracity of their message.

Christianity has been, of the three Western monotheisms, the one most intensely committed to spreading its religious truth among others. Christianity's early history and rise to power were entirely dependent on outreach to a variety of others. Beginning as a tiny sectarian group in first-century Palestine, Christianity spread via preaching to a multitude of audiences throughout the length and breadth of the Roman Empire. It was the attraction of increasingly large masses to the Christian faith that created the backdrop to the decision of the fourth-century Emperor Constantine to cease the persecution to which the young religion had been subjected and to set it on the road to becoming the ruling religion of the entire empire.