In Part III of Christianity and the Crisis of Cultures, Pope Benedict turns to the question of Christian faith: "the fundamental act of Christian existence."
Why, we might ask, does he choose to draw his reflections to a close by turning to the topic of faith? He actually gave us the answer toward the end of Part I.
Our greatest need in the present historical moment is people who make God credible in this world by means of the enlightened faith they live. We need men who keep their eyes fixed on God, learning from him what true humanity means (p. 52).
Faith, according to the Holy Father, is the way Christians strive to be fully human, the answer Christians give to the question: how can we fully realize our humanity?
Faced with western culture which, by and large, submerges humanity in a struggle for meaning in a world seemingly bereft of transcendence, Benedict says we must turn to faith in God. Faced with a Europe that suffers a tragic loss of memory of its Christian roots, thus threatening its own continued existence, the Pope urges a return to Christian faith. In the face of cultures which habitually regard human persons as objects, our best hope for recovering an enduring meaning for our lives, affirms Benedict, is a return to transcendence, to belief in God.
He begins by noting that we all share a commonsense notion of "faith" without which our lives would be rather difficult. When someone informs us that our expected time of arrival at Chicago O'Hare is 6:15pm, or tells us to take two tablets before going to bed, or that the fertility rate in France is on the rise—if the person who informs us has a reasonable degree of expertise (e.g., this person possess knowledge that we lack), we generally believe him or her. This kind of everyday "faith" is ubiquitous, and human life as we know it would be impossible without it.
This kind of everyday human "faith" is really more on the order of trust, and it relies on human knowledge: I may not know why or how X is the case, but someone does, so I therefore believe that X is the case.
It is precisely this kind of "faith" that raises a contemporary hurdle for the act of Christian faith:
This means that we are confronted once again, and in an even more urgent fashion, with the problem: Is this type of faith compatible with modern critical knowledge? Would it not be more appropriate for an adult of our times to refrain from expressing judgments on such matters and to wait for the day when science will have definitive answers even to this kind of question? (p. 84)
In other words, the Holy Father says the Christian is faced with a very peculiar contemporary challenge to his faith: is not a kind of devout agnosticism more reasonable? Rather than laying down claims about God and Revelation as answers to life's big questions, would it not be more reasonable respectfully to withhold any claims about such questions, allowing time and human knowledge to progress to the point of discovering alternative answers anchored in empirical reality? As Benedict puts it:
This, however, makes it all the more urgent to know whether the question of God does surpass the limits of human capabilities as such, so that agnosticism would in fact be the only correct attitude for man: the acknowledgment, appropriate and honest, "devout" in the profound meaning of that word, of that which eludes our grasp and our field of vision, a reverence vis-à-vis something that is inaccessible to us. Might not this be the new form of intellectual devotion: to leave aside whatever lies beyond our grasp and be content with what we are permitted to know? (p. 86)
The major contemporary challenge to Christian faith, then, is not atheism which lays down equally dogmatic and absolute claims about the non-existence of God—claims which cannot possibly be made with such quasi-scientific assurance. The challenge today, rather, is agnosticism anchored in Western pessimism about the possibilities and frontiers of human reason.