The wisest man preaches no doctrines; he has no scheme
 Henry David Thoreau, A Week on the Concord and Merrimack Rivers (1849). copy citation

Context

“But in all my wanderings I never came across the least vestige of authority for these things. They have not left so distinct a trace as the delicate flower of a remote geological period on the coal in my grate. The wisest man preaches no doctrines; he has no scheme; he sees no rafter, not even a cobweb, against the heavens. It is clear sky. If I ever see more clearly at one time than at another, the medium through which I see is clearer. To see from earth to heaven, and see there standing, still a fixture, that old Jewish scheme!” source