Life is a battle between faith and reason in which each feeds upon the other, drawing sustenance from it and destroying it.

The line frames human existence as a continual tension between two indispensable faculties: faith (trust, commitment, ultimate concern) and reason (critical inquiry, evidence, coherence). The paradox is that they are not simply enemies; each “feeds upon” the other. Reason can refine faith by exposing self-deception and sentimental piety, while faith can supply reason with moral purpose and the courage to act amid uncertainty. Yet the same interaction can become corrosive: reason can dissolve conviction into skepticism, and faith can overwhelm reason into dogmatism. The image of mutual sustenance and destruction captures a Niebuhrian realism about the fragility of human knowing and the need for humility in both belief and critique.