Most deists (see for instance Matthew Tindal's Christianity as Old as the Creation and Thomas Paine's The Age of Reason) saw the religions of their day as corruptions of an original, pure religion that was simple and rational. They felt that this original pure religion had become corrupted by "priests" who had manipulated it for personal gain and for the class interests of the priesthood in general.[20]

According to this world view, over time "priests" had succeeded in encrusting the original simple, rational religion with all kinds of superstitions and "mysteries" – irrational theological doctrines. Laymen were told by the priests that only the priests really knew what was necessary for salvation and that laymen must accept the "_mysteries" on faith and on the priests' authority. This kept the laity baffled by the nonsensical "mysteries", confused, and dependent on the priests for information about the requirements for salvation. The priests consequently enjoyed a position of considerable power over the laity, which they strove to maintain and increase. Deists referred to this kind of manipulation of religious doctrine as "priestcraft", a highly derogatory term. As Thomas Paine wrote:

As priestcraft was always the enemy of knowledge, because priestcraft supports itself by keeping people in delusion and ignorance, it was consistent with its policy to make the acquisition of knowledge a real sin.


This was ripped off Wikipedia