"The truths of religion are never so well understood as by those who have lost the power of reason"

Voltaire wields irony to suggest that certainty in religious “truths” often grows in inverse proportion to the use of reason. When rational scrutiny is suspended, belief becomes effortless; dogma no longer has to answer questions, and the believer experiences a powerful sense of clarity. That is precisely the “understanding” being mocked: not a hard-won comprehension tested by argument and evidence, but a confidence purchased by abandoning inquiry.

Reason introduces friction, questions about evidence, contradictions between doctrines, and the limits of human knowledge. It tolerates ambiguity and accepts that metaphysical claims may be undecidable. By contrast, credulity supplies quick resolutions. Authority, tradition, and emotion step in where proofs cannot. The result is a form of understanding that feels complete because it is no longer troubled by doubt. Voltaire exposes the danger: the less one thinks, the more one “knows.”

Underlying the aphorism is a critique of dogmatism. Religious institutions that discourage questioning cultivate a state in which the most zealous adherents appear most certain. Such certainty can be socially cohesive, but it risks fanaticism, intolerance, and the persecution of dissent. History supplied Voltaire with examples, and his barb urges vigilance against any system, sacred or secular, that rewards obedience over examination.

A charitable counterpoint notes that many spiritual traditions acknowledge the limits of reason and appeal to intuition or lived practice. Voltaire’s skepticism does not deny that faith can inspire moral insight or solidarity; it insists that these goods do not require the surrender of judgment. To call something true should not mean shielding it from critique.

The line ultimately champions intellectual humility. Where reason is active, beliefs are held lightly, revised when better arguments appear. Where reason is absent, beliefs harden into certainties immune to correction. Voltaire invites readers to seek whatever is valuable in religion through reflective, humane inquiry rather than through the counterfeit clarity of unreason.