Many people like to point out that the words "Separation of Church and State do not appear in the Constitution. Which seems odd to me, because I'm not aware of anyone who claims they do. But, just as "right to a fair trial" is not explicitly stated, but is still a fundamental cornerstone of our legal system, separation of Church and State is a fundamental cornerstone of our Government.
So where did the phrase come from, and what did Jefferson mean?
---chop--
Now, Thomas Jefferson was well known to be opposed to established religions, to the point where his opponents denounced him as an atheist during his Presidential campaign. After he won, the Danbury Baptist Association wrote him a letter congratulating him on his victory and expressing the hope of his positive influence on the states.
From the Danbury Baptist Association:
Our Sentiments are uniformly on the side of Religious Liberty—That Religion is at all times and places a Matter between God and Individuals—That no man aught to suffer in Name, person or effects on account of his religious Opinions—That the legetimate Power of civil Goverment extends no further than to punish the man who works ill to his neighbour: But Sir, our constitution of goverment is not specific. Our antient charter, together with the Laws made coincident therewith, were adopted as the Basis of our goverment, At the time of our revolution; and such had been our Laws & usages, & such still are; that religion is consider’d as the first object of Legislation; & therefore what religious privileges we enjoy (as a minor part of the State) we enjoy as favors granted, and not as inalienable rights: and these favors we receive at the expence of such degrading acknowledgements as are inconsistant with the rights of freemen. It is not to be wondred at therefore; if those, who seek after power & gain under the pretence of goverment & Religion should reproach their fellow men—should reproach their chief Magistrate, as an enemy of religion Law & good order because he will not, dares not assume the prerogative of Jehovah and make Laws to govern the Kingdom of Christ.
Sir, we are sensible that the President of the united States, is not the national Legislator, & also sensible that the national goverment cannot destroy the Laws of each State; but our hopes are strong that the sentiments of our beloved President, which have had such genial Effect already, like the radiant beams of the Sun, will shine & prevail through all these States and all the world till Hierarchy and tyranny be destroyed from the Earth
In his ]url=https://jeffersonpapers.princeton.edu/selected-documents/draft-reply-danbury-baptist-association]Draft Reply to the Danbury Baptist Association, Jefferson wrote:
Believing with you that religion is a matter which lies solely between man & his god, that he owes account to none other for his faith or his worship, that the legitimate powers of government reach actions only and not opinions, I contemplate with sovereign reverence that act of the whole American people which declared that their legislature should make no law respecting an establishment of religion, or prohibiting the free exercise thereof; thus building a wall of [eternal] separation between church and state. Congress thus inhibited from acts respecting religion and the Executive authorised only to execute their acts, I have refrained from prescribing even [those] occasional performances of devotion prescribed indeed legally where an Executive is the legal head of a national church, but subject here, as religious exercises only to the voluntary regulations and discipline of each respective sect.
Upon advice from Levi Lincoln, Jefferson removed that last sentence out of fear it would offend people who thought the President should pronounce days of Thanksgiving or prayer, especially those in New England, where such practice was common.
While your mileage may vary, my take is that Jefferson understood the Constitution to create a wall of separation by not allowing the government to use religion, or any religion to use the government, to support its own ends, but rather to keep the two spheres separate.
