While there is some truth in this statement, we should not take it at face value either. The period we call the Middle Ages is indeed a very religious one, not however because their predecessors had no faith in any god, but because the influence of the new faith went deeper and reached wider than before. The Christian Church reinvigorated the life of the whole Empire and the successor kingdoms, it reached to all social classes, and all had now the same understanding of the Just and Good. Yet, we are mistaken if we believe both that the people of Antiquity had less faith and more reason, while the people of the Middle Ages had less reason.
We are wrong because we fail to understand that ‘faith’ and ‘reason’ are two concepts that operate at two completely different levels of thought. If, as we usually believe, Ancient philosophy is the axiom of reason, we fail to understand what the object of the philosophical quest was. Socrates, Plato, Proclus, Plotinus, Aristotle, the Cynics, the Stoics, all had as their aim the search for God and the good life, which was precisely what the Christians believed had found.
Those who want to see in Christianity a triumph of obscure blindedness over reason should notice that in the arguments between Christians and ‘pagans’, no mention is made of “reason.” After Christ, the reasonable mind, which had hereto been given to the philosophical search, was simply redirected toward a more profound understanding of the revealed God–this is the nature of the Patristic texts.
The same holds true with the Renaissance. The Renaissance did not spring up suddenly from the ashes of the old monuments of Rome to usher a return to “reason.” Dante and Aquinas in their writings, Giotto in his paintings, were already in the 13th century–the century “par excellance” of the medieval era–developing certain features that would mark Western art and literature until our own days. Conversely, some of the greatest artworks of the Renaissance have biblical and other religious themes–unless we deny that the Sistine Chapel ceiling or the Annunciation of Da Vinci are work of the Renaissance. In the 16th century, some were considering a crusade against the menacing Turks.