James just quoted a paragraph from CS Lewis's Introduction to what was them a new edition of Athanasius, "On The Reading Of Old Books," and an excellent paragraph it is.
Nothing strikes me more when I read the controversies of past ages than the fact that both sides were usually assuming without question a good deal which we should now absolutely deny. They thought that they were as completely opposed as two sides could be, but in fact they were all the time secretly united—united with each other and against earlier and later ages—by a great mass of common assumptions. We may be sure that the characteristic blindness of the twentieth century—the blindness about which posterity will ask, “But how could they have thought that?”—lies where we have never suspected it, and concerns something about which there is untroubled agreement between Hitler and President Roosevelt or between Mr. H. G. Wells and Karl Barth. None of us can fully escape this blindness, but we shall certainly increase it, and weaken our guard against it, if we read only modern books.
If you ask me what those assumptions are, I will say it is a hundred things we do not notice, and I am not likely better at seeing such things as the next man. Yet I do think there is one difference among us that is growing, of those who live and breathe and have their being electronically and those who live lives more like our grandparents did. Yet none of us has lives very much like their grandparents, and they were the pivot generation that saw the introduction of flight, automobiles, radio, the telephone and some other major technological changes. There is more similarity in lives from 1900 backward, and we have been hopping for it ever since.