Augustine's "Confessions" and the beginning of self-consciousness.

As Cahill points out, Augustine of Hippo represents the first instance where self-conscience takes shape in Western literature:

If we page quickly through world literature from its beginnings to the advent of Augustine, we realize that with Augustine human consciousness takes a quantum leap forward —and becomes self-consciousness. Here for the first time is a man consistently observing himself not as Man but as this singular man —Augustine. From this point on, true autobiography becomes possible, and so does its near relative, subjective and autobiographical fiction.

(Cahill: p. 41)

Sure, before Augustine there were other instances of people writing about their experiences. However, the key was always the experiences themselves, the outside, the events. With Augustine, for the first time, it's the individual's concept of self, his own internal struggles and doubts, that is reflected on the page. Now, this would be a trivial issue if it weren't because the idea of individual is key to our civilization. Most people would agree that Western civilization is sustained on four legs: classical Antiquity (i.e., the Greek and Roman cultures), the Judeo-Christian tradition, the Age of Enlightenment and, finally, although directly linked to the previous one, modern Science. Well, in Augustine we find the first clear indication of the idea of individual, developed by the confluence between the classical civilization and both Judaism and Christianity. Neither the contemporary notion of human rights nor the idea of modern democracy would be possible without this accomplishment.

On how the Irish monks preserved Western civilization.

Thomas Cahill soon describes the core argument of this volume at the beginning of the book:

The word Irish is seldom coupled with the word civilization. (...) And yet... Ireland, a little island at the edge of Europe that has known neither Renaissance nor Enlightenment —in some ways, a Third World country with, as John Betjeman claimed, a Stone Age culture— had one moment of unblemished glory. For, as the Roman Empire fell, as all through Europe matted, unwashed barbarians descended on the Roman cities, looting artifacts and burning books, the Irish, who were just learning to read and write, took up the great labor of copying all of western literature -everything they could lay their hands on. These scribes then served as conduits through which the Greco-Roman and Judeo-Christian cultures were transmitted to the tribed of Europe, newly settled amid the rubble and ruined vineyards of the civilization they had overwhelmed. Without this Service of the Scribes, everything that happened subsequently would have been unthinkable. Without the Mission of the Irish Monks, who single-handedly refounded European civilization throughout the continent in the bays and valleys of their exile, the world that came after them would have been an entirely different one —a world without books. And our own world would never have come to be.

(Thomas Cahill: pp. 3-4)

We'll see later to what extent he manages to come up with clear evidence to back up these statements. However, it's true that until Cahill published this book the importance of the Irish contribution to Western civilization had not been stressed enough. Sure, there had been mentions here and there (Kenneth Clark's seminal work, Civilisation: A Personal View, deserves a special mention in this sense), but they had been ignored for the most part in favor of more familiar (and larger) countries. It is, unfortunately, a frequent bias in the study of History.