Reason, the Only Oracle of Man advances a robust program of natural religion in which unaided reason, observation, and moral sense—not miracle or ecclesiastical decree—ground humanity's knowledge of God and duty. Allen dismantles claims to special revelation, exposes contradictions in Scripture, rejects predestination and priestcraft, and posits a rational, benevolent moral order discernible in nature. Written in an energetic, frontier-inflected Enlightenment prose, the treatise stands within transatlantic deism while anticipating later American debates over revelation and religious liberty. Ethan Allen—a Revolutionary War hero and leader of the Green Mountain Boys—brought to this work the temper of a self-educated iconoclast. His frontier republicanism, hard-won distrust of hierarchical authority, and immersion in Enlightenment freethought shaped his critique of clergy and creeds. Written in the early national period, the book channels Allen's conviction that civic virtue and human happiness flourish when religion is accountable to reason. This volume rewards readers of intellectual history, theology, and American studies alike. Whether one shares its deism or not, Allen's lucid provocations sharpen thinking about authority, conscience, and evidence. It is essential for understanding the radical edge of early American religion and the prehistory of secular liberalism. Quickie Classics summarizes timeless works with precision, preserving the author's voice and keeping the prose clear, fast, and readable—distilled, never diluted. Enriched Edition extras: Introduction · Synopsis · Historical Context · Brief Analysis · 4 Reflection Q&As · Editorial Footnotes.