Edit: I see, Red Harvest has provided a basic major point here. Thank you.
And the term seperation of church and state was started in 1947 by a Supreme court judge who was also a former clansmen and hated the catholic church. I believe it had something to do with denying funds for religous schools.

Heres a goos artilce on the subject.

Separation of Church and State

In 1947, the Supreme Court attempted to define the "establishment of religion" clause of the First Amendment. Justice Hugo Black, writing for the court, held:


Neither a state nor the Federal Government can set up a church. Neither can pass laws which aid one religion, aid all religions, or prefer one religion over another. . . . In the words of Thomas Jefferson, the clause against the establishment of religion by law was intended to erect a "wall of separation between Church and State." [Everson v. Board of Education (1947).]