Interesting post. Actually, having read Spengler's original, rejected article, I have some bones to pick with it.
Spengler actually represents the other half of the problem that Pope Benedict was criticizing. He criticised religion without reason, and reason without religion. The problem in the West is that science and religion went their separate ways in the Renaissance and Reformation. The problem with Islam is that there simply is no place for rationality at all.
The Christian view is that human reason and rational order in the universe are a result of the way God created the universe. Particularly important is the idea of the Logos (Gospel of John, chapter 1).
I might say the same thing about Socrates. People differ about him, but Socrates was not merely IRONIC, as Spenger suggets. Socrates, like Plato, believed that at the highest levels, truth, beauty, and goodness converge. Socrates pursued truth, and he used the Socratic dialogue to clear away obstructions of the truth, not to deny that objective truth exists, which is the modernist position.
Similarly, there is much that is false and unscientific in modern "Scientific Bible Criticism." This movement can be traced back to Bismarck and his Kulturkampf, circa 1870. The first Professor of Modern Bible Studies in Germany was a Bismarck appointee, and his appointment was political, with an agenda.
Complicated matters. But Spengler completely misunderstands the issues at stake in Benedict's challenge.
The Christian view is that human reason and rational order in the universe are a result of the way God created the universe.
Are you trying to draw a distinction between "Reason" and "Rationality", and, if so, then what is the technical definition of "Reason", and what is the technical definition of "Rationality"?