"In an age when Christian thinkers were rediscovering the treasures of ancient philosophy, and more particularly of Aristotle, Thomas had the great merit of giving pride of place to the harmony which exists between faith and reason. Both the light of reason and the light of faith come from God, he argued; hence there can be no contradiction between them.
"More radically, Thomas recognized that nature, philosophy's proper concern, could contribute to the understanding of divine Revelation. Faith therefore has no fear of reason, but seeks it out and has trust in it. Just as grace builds on nature and brings it to fulfillment, so faith builds upon and perfects reason. Illumined by faith, reason is set free from the fragility and limitations deriving from the disobedience of sin and finds the strength required to rise to the knowledge of the Triune God. Although he made much of the supernatural character of faith, the Angelic Doctor did not overlook the importance of its reasonableness; indeed he was able to plumb the depths and explain the meaning of this reasonableness. Faith is in a sense an “exercise of thought”; and human reason is neither annulled nor debased in assenting to the contents of faith, which are in any case attained by way of free and informed choice." ~Fides et Ratio, no.43