In his book In the Beginning , Ratzinger writes:
“We must have the audacity to say that the great projects of the living creation are not the products of chance and error. Nor are they the products of a selective process to which divine predicates can be attributed in illogical, unscientific, and even mythic fashion. The great projects of the living creation point to a creating Reason and show us a creating Intelligence, and they do so more luminously and radiantly today than ever before. Thus we can say today with a new certitude and joyousness that the human being is indeed a divine project, which only the creating Intelligence was strong and great and audacious enough to conceive of. Human beings are not a mistake but something willed; they are the fruit of love. They can disclose in themselves, in the bold project that they are, the language of the creating Intelligence that speaks to them and that moves them to say: Yes, Father, you have willed me.”
Ratzinger argues that the appeal of Christianity in late antiquity was precisely its capacity to unite the desire of philosophers for a rational worldview based on perception and knowledge, as opposed to the irrational poetry of the gods, with the deepest longings of the human heart for truths about human existence. To allow a positivist philosophy of evolution to dislodge Christianity, he insists, would not be a victory for enlightenment, but ultimately the triumph of irrationality.
He makes this case in Truth and Tolerance:
"The question is whether reality originated on the basis of chance and necessity and, thus, from what is irrational; that is, whether reason, being a chance by-product of irrationality and floating in an ocean of irrationality, is ultimately just as meaningless; or whether the principle that represents the fundamental conviction of Christian faith and of its philosophy remains true - In principio erat Verbum - at the beginning of all things stands the creative power of reason. Now as then, Christian faith represents the choice in favor of the priority of reason and of rationality."