Age of Reason is a statement of belief in what Paine repeatedly calls the “true theology” of Deism. Rooted in scientific inquiry, Deism holds that one God created the universe and then left it alone to function according to natural laws discoverable by human reason. Paine champions Deism primarily because he believes it is true and, to a lesser degree, because it is useful.

The knowledge and reflections derived from celestial observation confirm the truth of Deism. Paine, in fact, identifies astronomy as “chief” in the “whole circle of science” (29). Astronomy is “the study of the true theology,” taught by the “Almighty lecturer” who has created “an immensity of worlds,” “moving orbs,” and “starry heavens” (33). This “mighty universe,” an “eternity of space, filled with innumerable orbs revolving in eternal harmony,” makes all other purported religions appear “paltry” by comparison (175).

There is also egalitarian beauty in Deism’s truth, for it is devoid of mystery and open to all: Paine touts the “pure and simple profession of Deism” (41). In Part 2, Paine pauses his analysis of the New Testament to contrast Christian ideas about the trinity (i.e. Father, Son, and Holy Spirit) with the “plain, pure, and unmixed belief of one God, which is Deism” (128, emphasis added).