''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, & 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 & State''-Thomas Jefferson, 1802.
The 'establishment of religion' clause of the First Amendment means at least this:
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. Neither can force nor influence a person to go to or to remain away from church against his will or force him to profess a belief or disbelief in any religion. No person can be punished for entertaining or professing religious beliefs or disbeliefs, for church attendance or non-attendance. No tax in any amount, large or small, can be levied to support any religious activities or institutions, whatever they may be called, or whatever from they may adopt to teach or practice religion.
Neither a state nor the Federal Government can, openly or secretly, participate in the affairs of any religious organizations or groups and vice versa. In the words of Jefferson, the clause against establishment of religion by law was intended to erect 'a wall of separation between Church and State.' Reynolds v. United States, supra, 98 U.S. at page 164, 25 L.Ed. 244.-Justice Hugo Black
en.wikipedia.org
Stone v. Graham, 449 U.S. 39 (1980), was a court case in which the
Supreme Court of the United States ruled that a
Kentucky statute was unconstitutional and in violation of the
Establishment Clause of the First Amendment, because it lacked a nonreligious, legislative purpose. The statute required the posting of a copy of the
Ten Commandments on the wall of each public classroom in the state. The copies of the Ten Commandments were purchased with private funding, but the Court ruled that because they were being placed in public classrooms they were in violation of the
First Amendment.