‘Separation of church and state’ metaphor rooted in early American fears of government involvement
Roger Williams, founder of Rhode Island, was the first public official to use this metaphor. He opined that an authentic Christian church would be possible only if there was “a wall or hedge of separation” between the “wilderness of the world” and “the garden of the church.” Williams believed that any government involvement in the church would corrupt the church.
The most famous use of the metaphor was by Thomas Jefferson in his 1802 letter to the Danbury Baptist Association. In it, Jefferson declared that when the American people adopted the establishment clause they built a “wall of separation between the church and state.”
Jefferson had earlier witnessed the turmoil of the American colonists as they struggled to combine governance with religious expression. Some colonies experimented with religious freedom while others strongly supported an established church.
Thomas Jefferson “separation of church and state”
Thomas Jefferson created the most famous use of the metaphor “separation of church and state” in a letter where he mentioned a “wall of separation.” (Image via White House Historical Association, painted by Rembrandt Peale in 1800, public domain)
Jefferson fought to disestablish Anglican church in Virginia colony
One of the decisive battlegrounds for disestablishment was Jefferson’s colony of Virginia, where the Anglican Church had long been the established church.
Both Jefferson and fellow Virginian James Madison felt that state support for a particular religion or for any religion was improper. They argued that compelling citizens to support through taxation a faith they did not follow violated their natural right to religious liberty…
https://firstamendment.mtsu.edu/article/establishment-clause-separation-of-church-and-state/