During his long career as a strong defender of the notion of "Christian philosophy", Etienne Gilson (1884-1978) maintained a firm stance in his belief in the intrinsic, essential and constitutive influence of Christian revelation on medieval philosophy. As both an historian of medieval philosophy and as a student of St. Thomas Aquinas, Gilson believed strongly in both the formal distinction and the profound continuity, harmony and collaboration between faith and reason, philosophy and theology, and nature and grace in the doctrine of St. Thomas. In his effort to discover beyond the traditions of Thomistic commentators the personal thought of St. Thomas himself, Gilson often had to swim against a prevailing rationalistic current which sought to separate the philosophy of St. Thomas from the theology in which alone it could retain its viability and fruitfulness. But he refused to separate in the name of St. Thomas what St. Thomas himself not only did not separate but offered positive evidence against separating. There is an historical reason therefore for not separating the personal philosophy of St. Thomas from his theology. Thomas himself never did it. This erroneous tendency of separating the two sciences inevitably then leads to other, even greater and more harmful errors in both philosophy and theology, as the principle states, "Parvus error in principio magnus est in fine" (a small error in the beginning becomes a large error in the end, that is to say, when it is carried to its logical conclusion). And in Gilson's opinion, this unnatural separation is not a small error, but already a large and dangerous one. The Thomistic doctrine on the role of sacred doctrine, understood in its full transcendent sense, along with the celebrated Thomistic principle: "grace does not destroy nature but perfects it" (Summa Theologiae., I, 1, 8, ad 2), were for Gilson the central guiding principles which shed light on the relationship between faith and reason in St. Thomas. To Gilson these principles are often misunderstood and distorted by even professed followers of St. Thomas, and he believed that only by returning to their full original significance as understood and taught by St. Thomas can the unhealthy rupture between philosophy and theology be healed. And only by restoring to theology its pristine and rightful position as guiding light can philosophy attain its noble and exalted status as handmaiden within the royal kingdom of divine science. This book is an expanded version of the author's Licentiate thesis in philosophy, for which he received the highest marks possible. If you like this book or any other of the books I've written or edited, please leave a positive review, so that others may profit by them, and also that this struggling author and editor may continue to do this work for the glory of God. May He bless and protect you and yours.