I must begin with the words of the clergyman: ‘My short sermon for today is divided into three parts. One: God. Two: Man. Three: The Universe.’ It will be impossible to do justice to the subject in hand in the short span of one lecture. This is not only because of the vast range of time and space involved in any consideration of the parting of the ways between eastern and western Christianity in the late antique period. To embark on such a theme involves holding up for scrutiny the very nature of ecclesiastical history. For what we have to deal with is not merely what happened in the relations between east and west, but why what happened happened as it did. Once the ecclesiastical historian asks why, he will find himself sooner or later forced to grapple with the whole quality of men’s lives in the past—that is, with how they lived the full twenty-four hours of the day, not only in their books, but in their churches, not only in their churches, but in the most intimate and most monotonous rhythms of their life.