Cambridge History of American Literature: volume 1, Colonial and Revolutionary Literature: Early National Literature: Part I
Trent, William Peterfield, 1862-1939., Erskine, John, 1879-1951., Sherman, Stuart Pratt, 1881-1926., Van Doren, Carl, 1885-1950., Ed.

If Margaret Fuller is the literary critic of transcendentalism, Theodore Parker (1810-1860) is its theologian and reformer. Parker was a graduate of Harvard and of the Harvard Divinity School, and held pastorates near or in Boston during the whole of his ministerial career. He carried to its extreme form the theological reaction from eighteenth-century Unitarianism begun by Channing, his South Boston sermon in 1841 on The transient and permanent in Christianity being generally considered a milestone not only in the history of transcendentalism but in the development of American theology.

Parker, though his nature was not lacking in qualities of engaging simplicity and kindliness, was a man of warlike and aggressive temperament, of indomitable energy whether in thought or action, “our Savonarola,” as Emerson called him. During the earlier part of his life, much of his tremendous power of activity was expended upon books, and he became a man of immense erudition, the most widely read member of the transcendental group. His learning, however, savoured a little too much, as Lowell suggested, of an attempt to tear up the whole tree of knowledge by the roots, and he surely misconstrued his own nature when he declared “I was meant for a philosopher, and the times call for a stump orator.” His mind was in reality more practical than metaphysical in its cast, and it was with the turning of his interest to the slavery question and especially with the arousing of all the fires of his nature at the passage of the Fugitive Slave Law that the tremendous will power and earnestness of the man came out to the full. During the years of this controversy, he interspersed an endless mass of correspondence, lectures, sermons, and addresses with deeds of conspicuous moral and physical courage. He was chairman of the executive committee of the Vigilance Committee, sheltered fugitive slaves in his own house and aided their escape in all ways possible, was indicted but never brought to trial in connection with the famous Burns Affair, and came into intimate relations with John Brown. It was the strain of labours of this sort that led to his premature death in 1860.

These anti-slavery activities of Parker came, of course, after the crest of the transcendental movement, but they are mentioned here as an illustration of that tendency in transcendentalism,