The phrase originates in Thomas Jefferson's 1802 letter to the Baptist Association of Danbury, Connecticut. Jefferson was responding to the Danbury Baptists' complaints that Connecticut's law was oppressive to their religion (among other things, Connecticut's law allowed towns to levy taxes for the support of a religion designated by the majority of voters; since Connecticut was overwhelmingly Congregationalist, the law effectively forced Baptists throughout the state to support Congregational churches). The Baptists, who knew of Jefferson's advocacy of separation, "honored [Jefferson] as an apostle of religious liberty. Much of their address sounded like [Jefferson's] bill for establishing religious freedom in Virginia, and they hoped that the sentiments of their 'beloved President' would prevail so that 'hierarchy and tyranny' would vanish from the earth" (Dumas Malone, Jefferson the President: First Term, 1801-1805, p. 109).
While Jefferson was powerless to change Connecticut's law (the First Amendment did not yet apply to the states), Jefferson used the occasion to express his belief that no such law could be implemented on the federal level. Observed Jefferson:
I contemplate with sovereign reverence that act of the whole American people which declared that their legislature should "make no law regarding an establishment of religion, or prohibiting the free exercise thereof," thus building a wall of separation between Church and State.
Separationists have long taken Jefferson's "wall" metaphor as an accurate and historically significant summary of the intent of the First Amendment. Indeed, we take the metaphor so seriously that we are sometimes accused of worshipping Jefferson, as if the only reason we think the Constitution requires the separation of church and state is because Jefferson wrote his letter. But this is nonsense; the history of the Constitution and the First Amendment is well documented, and it suggests beyond doubt that the framers wanted to put as much distance between government and religion as possible. Jefferson's metaphor is simply a handy way of stating the obvious. If Jefferson had never written his letter, we would still be defending the wall, since the wall exists in the Constitution itself.
We consider and refute three other charges against Jefferson's wall metaphor elsewhere in this web page. If you want to read these sections now, click here, here, and here.