(_b_) We take with us in our travels into the past the underlying conception of religion as a personal bond between God and the individual soul. We cannot believe that there is any virtue in an act of worship in which the conscience has no place. We can understand, however much we may deplore, such persecutions as those of the sixteenth century, because they ultimately rest upon the same conception: men were so profoundly convinced of the truth of their own personal beliefs as to deem it of supreme importance that other men should hold those beliefs also. But we find it difficult to understand why, in the second century of our era, a great emperor who was also a great philosopher should have deliberately persecuted Christianity. The difficulty arises from our overlooking the entirely different aspect under which religion presented itself to a Roman mind. It was a matter which lay, not between the soul and God, but between the individual and the State. Conscience had no place in it. Worship was an ancestral usage which the State sanctioned and enforced. It was one of the ordinary duties of life.[8] The neglect of it, and still more the disavowal of it, was a crime. An emperor might pity the offender for his obstinacy, but he must necessarily either compel him to obey or punish him for disobedience. * * * * * It is not until we have thus realized the fact that the study of history requires as diligent and as constant an exercise of the mental powers as any of the physical sciences, and until we have made what may be called the “personal equation,” disentangling ourselves as far as we can from the theories which we have inherited or formed, and recognizing the existence of under-currents of thought in past ages widely different from those which flow in our own, that we shall be likely to investigate with success the great problem that lies before us. I lay stress upon these points, because the interest of the subject tends to obscure its difficulties. Literature is full of fancy sketches of early Christianity; they are written, for the most part, by enthusiasts whose imagination soars by an easy flight to the mountain-tops which the historian can only reach by a long and rugged road; they are read, for the most part, by those who give them only the attention which they would give to a shilling hand-book or to an article in a review. I have no desire, and I am sure that you have no desire, to add one more to such fancy sketches. The time has come for a precise study. The materials for such a study are available. The method of such a study is determined by canons which have been established in analogous fields of research. The difficulties of such a study come almost entirely from ourselves, and it is a duty to begin by recognizing them.