William Ellery Channing (1780-1842) helped Unitarians to see themselves as a distinct denomination (rather than merely the liberal wing of the congregational church). He was pastor of Federal Street (now Arlington Street) Church, and was the first to define Unitarian theology in a comprehensive way in his 1819 sermon entitled “Unitarian Christianity,“ known to many UUs as “The Baltimore Sermon.” It was largely due to his leadership that the American Unitarian Association was formed in Boston in 1825.
“All that a man does outwardly is but the expression and completion of his inward thought. To work effectually, he must think clearly; to act nobly, he must think nobly. Intellectual force is a principal element of the soul's life, and should be proposed by every man as the principal end of his being."