In 1801, members of the small Baptist church in Danbury, Connecticut, wrote a letter to President Thomas Jefferson (1743-1826) congratulating him on his recent election. At the time, Baptist’s were a minority religion. In New England the Congressional Church was prominent. Jefferson assured them that they had nothing to worry about. Their letter had expressed worries about being in the minority. They were afraid they would lose their rights and be forced to become Congregationalists.
A few months later, the President answered their letter. jefferson said,in effect, that the First Amendment to the Constitution had erected a “wall of separation” between church and state that meant Connecticut could not interfere with the Baptist’s religious freedom.
“Believing with you that religion is a matter with lies solely between Man and 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 separation between Church and State.
Jefferson’s metaphor of the wall between church and state became enormously influential, Although not part of the Constitution, Jefferson’s metaphorical wall has been recognized by the Supreme Court as a guiding concept in the relationship between church and state. It has been cited by many American political and religious leaders.
Jefferson’s letter remains a cornerstone, an influential interpretation of First Amendment cause and a cornerstone of religious liberty in the United States.

President Thomas Jefferson