They get paid for it. Think about it. If you thought so little of your fellow man, that you would enslave his mind, and eat the fruits of his labor, while peddling a snake oil solution to his problems (ensuring he would always have to come back for more), you'd be a priest.

As it stands, I believe parts of the Bible (New Testament), read, allowing for interpretation as a thinking man, not as a pawn, that when their savior returns, they intend to divide up the cities, the cities' wealth, and its inhabitants, according to who has promoted their religion the best. And parts of Revelation seem to imply that these priests will have the 'true believers' tackle an army of superior numbers and strength, with the promise that this is 'the first death.' Me thinks the priests have found an excellent way of killing off select portions of the populace, and claiming their belongings in their absence.

What these 'true believers' are told, is that 1.) in attacking this army, they are doing the will of their god, and 2.) that by doing so, they will earn favor with their god, and so are assured a 'resurrection,' which will take place at some point in the future (several years, or a thousand, who knows), and 3.) the army that they attacked will be thrown into a volcano pit ('the second death').

Given that quite a few of the Abrahamic religions all state something similar, and I may have found traces in a few other religions, I feel I am either looking at a poison pill / scorched earth scenario, in which the religion is attempting to protect itself against a hostile takeover from another, or someone has setup an interesting doomsday scenario, where a few fires in the right places, maybe a timely famine, and a shout of 'the enemy is over the next ridge,' with no clue who that enemy is, resulting in two or more groups annihilating each other in the process. It would be an intriguing solution to the 'population problem,' while 'cleansing' the earth / human gene pool of less desirables (anyone who doesn't resist the religion a.k.a. the mentally enfeebled).

I'm still weighing a few things, mentally, with regards to this...I could be wrong, and probably am.