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 that aid one religion, aid all religions, or prefer one religion to 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. 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."
Everson v. Board of Education, 330 U.S. 1, 1947.