William Bentley, pastor in Salem, Massachusetts from 1783 to his death in 1819, was unlike anyone else in America's founding generation, for he had come to unique conclusions about how best to maintain a traditional understanding of Christianity in a world ever changing by the forces of the Enlightenment.

Like some of his contemporaries, Bentley preached a liberal Christianity, with its benevolent God and salvation through moral living, but he-and in New England he alone-also preached a rational Christianity, one that offered new and radical claims about the power of God and the...