The following quotation is from John M. Oesterreicher, The Walls are Crumbling: Seven Jewish Philosophers Discover Christ, London: Hollis and Carter, 1953, p. 195. Oesterreicher is glossing Landsberg's doctoral thesis Wesen und Bedeutung der Platonischen Akademie, 1923:
. . . there are two types of philosophy: the autonomous, patterned after Plato's, which undertakes to bring about man's redemption; and the heteronomous, which, following St. Augustine's lead, does not feign to be man's guide to his last end, but takes him to the very portals of faith, and there wthdraws before the one thing necessary.
Ah, but what is the one thing necessary?
There is a tension between the two types of philosophy and this tension is the transposition onto the philosophical plane of the tension between Athens (Greek philosophy) and Jerusalem (the Bible), the two main roots of the West whose fruitful entanglement is the source of the West's vitality. As Leo Strauss sees it, it is a struggle over the unum necessarium, the one thing needful or necessary:
To put it very simply and therefore somewhat crudely, the one thing needful according to Greek philosophy is is the life of autonomous understanding. The one thing needful as spoken by the Bible is the life of obedient love. The harmonizations and synthesizations are possible because Greek philosophy can use obedient love in a subservient function, and the Bible can use philosophy as a handmaid; but what is so used in each case rebels against such use, and therefore the conflict is really a radical one. ("Progress or Return?" in The Rebirth of Classical Political Rationalism, University of Chicago Press, 1989, p. 246, bolding added.)
So is the Christian the true philosopher? Only in the sense that philosophy points beyond itself to something that is no longer philosophy but that completes philosophy while cancelling it. I am tempted to reach for an Hegelian trope while turning it on its head: if Christianity is true, then philosophy is aufgehoben, sublated, in it. If Christianity is true, then the Christian arrives at the truth that the philosopher at best aims at but cannot arrive at by his method and way of life, the life of autonomous understanding. To achieve what he aims at, the philosopher would have to become "as a little child" and accept in obedient love the gift of Revelation. But it is precisely that which he cannot do if he is to remain a philosopher in the strict sense, one who lives the life of autonomous understanding.
This is tension some of us live. The life of autonomous understanding and critical examination? Or the life of child-like trust and obedient love?
The problem in what is perhaps its sharpest form is presented in the story of Abraham and Isaac.
The Christian life is not the philosophical life. It lies beyond the philosophical life and, if true, is superior to it.
But is it true?
In the end, you have to decide what you will believe and how you will live.
Some extensive quotation from the neglected Landsberg in Kant on Suicide.