Philosophy is Necessarily Christian --Pieper

"'Christian philosophy' is not a more or less abstruse brand of philosophical activity corresponding to the special ('religious') interests of individuals. It is the only possible form of philosophy--if it is true that the Logos of God became man in Christ, and if by 'philosophy' we understand what the great forefathers of European philosophizing (Pythagoras, Plato, Aristotle) meant by it. The thinkers of the Middle Ages perceived that a 'Christian philosophy' depended upon the conjunction of fides and ratio. This was the task they set themselves, and into this task they poured their full intellectual resources. This task is continuous and never-ending. Anyone who addresses himself today to this same task cannot afford to ignore the demanding and multiform paradigm of medieval philosophy. But in answer to the questions posed he cannot take the medieval view; he will have to find his own answer."
Josef Pieper, Scholasticism, New York: McGraw-Hill, 1964, 162.

Philosophy is the slave of the Deposit of Faith and the Deposit of Faith is the slave of Philosophy, both being bound to the Truth. Rupture of that mutual servitude causes the pathologies peculiar to faith without reason and reason without faith.
Cf. Joseph Ratzinger: The Dialectics of Secularization, San Francisco: Ignatius, 2006, 77-80.