The positive doctrine is set out in Emerson essay Nature of 1836. The natural world is not merely useful and not merely beautiful; it is a language, in which particular facts stand for particular spiritual facts, so that reading nature attentively is a form of revelation available to anyone with eyes. Thoreau took the claim literally enough to test it, living beside Walden Pond for two years and writing the book that came out of it, which is at once a natural history, an economic argument and a religious exercise.
The movement had no creed and no organisation, only a discussion club, a journal called The Dial edited first by Margaret Fuller and then by Emerson, and a set of friendships. Fuller Woman in the Nineteenth Century came out of the same circle and is among the first substantial American works of feminist argument.
The Dial ran a series of extracts under the heading Ethnical Scriptures, printing passages from the Laws of Manu, from Confucius and from Buddhist material beside Western sources, and treating them as scripture rather than as anthropological curiosity. Emerson read the Bhagavad Gita and the Upanishads in the translations then available and wrote the poem Brahma out of them; Thoreau kept a copy of the Gita at Walden. The reading was selective and filtered through idealist assumptions, but it was the first sustained American engagement of its kind, and the later American reception of Asian religion runs back through it.