When seeking to discern people's religious beliefs, we must let them speak for themselves. The best, most succinct, understanding of Jefferson's religious beliefs was clearly spelled out in a letter he wrote at Monticello in his older years (June 26, 1822) to Dr. Benjamin Waterhouse.
In the letter, Jefferson was very candid. He said the true, reliable doctrines of Jesus were: 1) There is only one God; He is all perfect; 2) There is a future state of rewards and punishments; 3) To love God with all thy heart, and thy neighbor as thyself, is the sum of religion.
To make doubly sure he was clearly expressing his beliefs, Jefferson in the same letter absolutely rejected Calvinism, saying it wrongly taught: 1) There are three Gods; 2) Good works are nothing; 3) Faith is everything; 4) Reason in religion is unlawful; 5) God elected certain individuals to be saved, and certain others to be damned.
In this letter, Jefferson called himself a Unitarian, and wrote, "I trust that there is not a young man now living in the United States who will not die an Unitarian." I think this designation of himself as a Unitarian is, in modern parlance, the most accurate description of his religious beliefs.
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