After the material unity, after the political, there should have been formed the moral and intellectual; but at this point, the forces of Rome gave way. Rome had gathered under its sceptre too many races, too many kinds of culture, religions too diverse; its spirit was too exclusively political, administrative, and judicial; it could not therefore conciliate the ideas, assimilate the customs, weld the sentiments, unify the religions, by its laws and decrees. To this end was necessary the power of ideas, of doctrines, of beliefs that officials of administration could neither create nor propagate. The work was to be accomplished outside of, and in part against, the government. It is the work of Christianity.
Many have asked me how I shall consider Christianity in the sequence of my work. In brief, I may say that I shall follow a different method from that which its historians have taken up to this time: they have studied especially how there was formed that part of Christianity which yet lives and is the soul of it, namely, the religious doctrine. On this account, they generally separate its history from the history of the Empire, making of it the principal argument, considering the history of Roman society as subordinate to it and therefore only an appendix. I propose to reverse the study, taking Christianity as a chapter, important but separate, in the history of the Empire. If for three centuries Christianity has been gradually returning to its origin, that is, becoming purely a religion and a moral teaching, for some centuries in the ancient world it was a thing much more complicated; a government and an administration that willed not only to regulate the relations between man and God, but to govern the intellectual, social, moral, political, and economic life of the people! The historian ought to explain how this new Empire—for it was indeed a new Empire—was formed in Rome and upon its ruins: this is a problem much more intricate than at first appears.