It is manifest that the reasons that may induce a ruler to suppress by force some forms of religious worship or opinion, are very various. He may do so on moral grounds, because they directly or indirectly produce immorality; or on religious grounds, because he believes them to be offensive to the Deity; or on political grounds, because they are injurious either to the State or to the Government; or on corrupt grounds, because he desires to gratify some vindictive or avaricious passion. From the simple fact, therefore, of a religious persecution we cannot at once infer the principles of the persecutor, but must examine in detail by which of the above motives, or by what combination of them, he has been actuated. Now, the persecution which has taken place at the instigation of the Christian priests differs in some respects broadly from all others. It has been far more sustained, systematic, and unflinching. It has been directed not merely against acts of worship, but also against speculative opinions. It has been supported not merely as a right, but also as a duty. It has been advocated in a whole literature of theology, by the classes that are especially devout, and by the most opposing sects, and it has invariably declined in conjunction with a large portion of theological dogmas. I have elsewhere examined in great detail the history of persecutions by Christians, and have endeavoured to show that, while exceptional causes have undoubtedly occasionally occurred, they were, in the overwhelming majority of cases, simply the natural, legitimate, and inevitable consequence of a certain portion of the received theology. That portion is the doctrine that correct theological opinions are essential to salvation, and that theological error necessarily involves guilt. To these two opinions may be distinctly traced almost all the sufferings that Christian persecutors have caused, almost all the obstructions they have thrown in the path of human progress; and those sufferings have been so grievous that it may be reasonably questioned whether superstition has not often proved a greater curse than vice, and that obstruction was so pertinacious, that the contraction of theological influence has been at once the best measure, and the essential condition of intellectual advance. The notion that he might himself be possibly mistaken in his opinions, which alone could cause a man who was thoroughly imbued with these principles to shrink from persecuting, was excluded by the theological virtue of faith, which, whatever else it might involve, implied at least an absolute unbroken certainty, and led the devotee to regard all doubt, and therefore all action based upon doubt, as sin.