Unlike Christian Byzantium, Christian Rome represents only a brief interlude between paganism and barbarism. There were only eighteen years between Theodosius’s closing of the temples and the first sack of the Eternal City by the barbarians. The great age of the Western Fathers from Ambrose to Augustine was crammed into a single generation, and St. Augustine died with the Vandals at the gate.
Then:
In the Dark Ages the saints were not merely patterns of moral perfection, whose prayers were invoked by the Church. They were supernatural powers who inhabited their sanctuaries and continued to watch over the welfare of their land and their people….
Nevertheless it was only in this world of Christian mythology—in the cult of the saints and their relics and their miracles—that the vital transfusion of the Christian faith and ethics with the barbaric tradition of the new peoples of the West could be achieved. It was obviously impossible for peoples without any tradition of philosophy or written literature to assimilate directly the subtle and profound theological metaphysics of a St. Augustine or the greater teachers of the Byzantine world. The barbarians could understand and accept the spirit of the new religion only when it was manifested to them visibly in the lives and acts of men who seemed endowed with supernatural qualities. The conversion of Western Europe was achieved not so much by the teaching of a new doctrine as by the manifestation of a new power, which invaded and subdued the barbarians of the West, as it hard already subdued the civilized lands of the Mediterranean. And as the martyrs had been the heroes and witnesses of the conquest of the Empire, so it was the hermits and the monks who were the confessors and apostles of the faith among the barbarians.
Here the relation between religion and culture is not that of assimilation and permeation, but rather one of contradiction and contrast. The lives of the saints and ascetics impressed the mind of the barbarians because they were the manifestation of a way of life and a scale of values entirely opposed to all they had hitherto known and accepted. But the contrast was not between the higher civilization of the Christian Roman world and the barbarism of the pagans, but a contrast between two spiritual worlds or two planes of reality. For behind the ethical contrast between the life of the saint and the barbarism of society there lies the eschatological dualism of the present world and the world to come which was the background of the medieval Christian view of life.
The Western Church did not come to the barbarians with a civilizing mission or any conscious hopes of social progress, but with a tremendous message of divine judgment and divine salvation. Humanity was born under a curse, enslaved by the dark powers of cosmic evil and sinking ever deeper under the burden of its own guilt. Only by the way of the Cross and by the grace of the crucified Redeemer was it possible for men to extricate themselves from the massa damnata of unregenerate humanity and escape from the wreckage of a doomed world.