Unitarianism emerged from Congregationalism in the early nineteenth century. A religion of reason, it sought to subject the Bible and Christianity to the bar of reason. Atonement does not require God to execute an innocent being, they insisted. Man can turn to the God of love on his own ability. They distilled the Christian faith to "The Fatherhood of God, The Brotherhood of Man and the Leadership of Christ." 

Transcendentalists were united by the belief that we all possess a divine spark, and that human beings enter the world trailing clouds of glory. This purity and innocence is lost over time, and salvation (if you can call it that) consists of connecting once again with the divinity within us.  The response of the old line Unitarians to such ideas was to charge the Transcendentalists with infidelity. Clearly, this new liberalism had affinities with the old:

(1) both accented divine benevolence,

(2) both attacked traditional trinitarianism

(3) both affirmed the essential divinity of man, and

(4) both rejected classical theories of the atonement.

On other hand, Transcendentalists went far beyond the Unitarians in four ways. They believed in:

(1) divine immanence

(2) intuitive perception

(3) rejection of external authority and

(4) a radical social ethic. 

Ralph Waldo Emerson entered Harvard Divinity School in 1825. At the time, it was dominated by two liberals: Henry Ware and Andrews Norton. The faculty was well satisfied with the traditional tenets of rational Christianity, but not Emerson. He never finished his degree. He refused to be a spiritual pensioner on his ancestors. Instead, he choose to strike out on his own in an effort to find a more vital faith. The church as he knew it was dead. Emerson was looking for a vital, lively faith. 

In 1826, Emerson applied for a license to preach at the Middlesex Association of Ministers. The trial sermon he submitted was on the text in I Thessalonians 5:17 "Pray without ceasing." In this introduction to this sermon, Emerson laid out two basic philosophical ideas that would come to characterize his mature religious thought: (1) the primacy of spirit over matter; and (2) the immediacy of God to the human soul.

The God of the Transcendentalists sustained an intimate relation to the world of nature and of man. This God immanently vitalizes the whole cosmos, and especially the human soul. Emerson wrote that "God is the substratum of all souls." At another point, he said, "the soul is the Kingdom of God, the abode of love of truth, of virtue." (Journals II, 361) The only proof of God, they argued, was in our moral instincts. 

The Transcendentalists stood to the left of the Unitarians in their social thinking. If every man has within him Divine reason, they contended, every person must be free to realize their fullest potentiality. If people could reach their fullest potential, then it would be possible to realize Heaven on Earth. Therefore, the Transcendentalists were reformers. War, capitalism, intemperance, and slavery found some their greatest enemies among the Transcendentalists. 

Brook Farm was an effort by the Transcendentalists to frame a new society. This effort was also part of a broader movement toward French utopian socialism in the intellectual circles of the 19th century. The principles for this new community were simple: each person was to contribute what one could; all work had its own dignity; and each person was to be as self-reliant as possible. As Emerson had put it, in relying on the true self, one relies on God. (Or to put it another way, if one peels the onion of the self, one finally gets to Ultimate Reality.) 

Brook Farm was a hit among the cultural elite. Nathaniel Hawthorne, for instance, was in residence for a while. The community was also distinguished by its interest in education. One of those in residence who explored new educational ideas was Bronson Alcott. His work was built on the principle that since the mind comes from God, education should teach people how to attach themselves to the Spirit.