A conservative, Gannett was not an admirer of the Transcendentalist movement. The Memoir, written by Gannett's son (who was) is fascinating on the rise of Transcendentalism and its impact on Unitarianism. An excerpt...
"Viewed as a school of philosophy, the Transcendentalists were simply the little New England quota in the great return of thinkers to Idealism, after the long captivity to Sensationalism. Returns almost inevitably have the exaggeration and one-sidedness of reaction. The new king usurps entire allegiance, whereas allegiance seems due to one who rules at once both kingdoms, Intuition and Experience. As a school of critics, they were the earliest here who boldly used the modern historic method in the study of the Bible. As a school of theology, they dispensed with Mediation, in order to claim for the soul access direct to its Father. They have been credited with bringing the doctrine of the Holy Spirit into the Unitarian "common sense in religion." But more than the common doctrine of the Holy Spirit, and more than Orthodoxy compassed by its faith in Incarnation and the Helping Grace, their thought really implied. It implied a universal law of access and communion. It affirmed abiding contact of the finite and the Infinite in virtue of the very nature of the soul and Over-Soul. Inspiration fresh as well as old; Revelation constant; Miracle but the human spirit's pinnacle of action ; God the living God, not a deity then and there announcing himself with evidence of authenticity, but indwelling here and now in every presence, — this was " Transcendentalism."
(for more on the Holy Spirit, see today's post at Wonderful Epoch)