Well, legally speaking, you can thank the U.S. Supreme Court in its decision of Marsh v. Chambers 463 U.S. 783 (1983). At issue in this case was the Nebraska legislature’s practice of praying before opening legislative sessions. The prayer was led by a chaplain paid for by the taxpayers. This is a practice the First Congress of the United States began approximately in 1789. Chief Justice Warren Burger wrote for the majority.
Chief Justice Burger employed a method of interpreting the Establishment Clause which today can be accurately characterized as Originalism. Chief Justice Burger focused upon the long tradition of opening session of government with a formal prayer. More important to Chief Justice Burger’s argument was the fact the First Congress, comprised of many Founding Fathers and Framers to the U.S. Constitution, passed legislation establishing opening sessions of Congress with a moment of prayer led by a chaplain and paying them from the national treasury. "*On September 25, 1789, three days after Congress authorized the appointment of paid chaplains, final agreement was reached on the language of the Bill of Rights, S. Jour., supra, at 88; H. R. Jour., supra, at 121. 9 Clearly the men who wrote the First Amendment Religion Clauses did not view paid legislative chaplains and opening prayers as a violation of that Amendment, for the practice of opening sessions with prayer has continued without interruption ever since that early session of Congress…
In this context, historical evidence sheds light not only on what the draftsmen intended the Establishment Clause to mean, but also on how they thought that Clause applied to the practice authorized by the First Congress - their actions reveal their intent. An Act passed by the first Congress assembled under the Constitution, many of whose members had taken part in framing that instrument, . . . is contemporaneous and weighty evidence of its true meaning." Wisconsin v. Pelican Ins. Co…
It can hardly be thought that in the same week Members of the First Congress voted to appoint and to pay a chaplain for each House and also voted to approve the draft of the First Amendment for submission to the states, they intended the Establishment Clause of the Amendment to forbid what they had just declared acceptable. In applying the First Amendment to the states through the Fourteenth Amendment, Cantwell v. Connecticut, 310 U.S. 296 (1940), it would be incongruous to interpret that Clause as imposing more stringent [463 U.S. 783, 791] First Amendment limits on the states than the draftsmen imposed on the Federal Government.
This unique history leads us to accept the interpretation of the First Amendment draftsmen who saw no real threat to the Establishment Clause arising from a practice of prayer similar to that now challenged.
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Summation…the original meaning of the Establishment Clause does not prohibit the practice of opening sessions of the legislature with a moment of prayer by a chaplain paid for by taxpayers’ dollars. This is precisely the argument Justice Scalia made in his dissent in the Ten Commandment case of McCreary County v. ACLU of Kentucky, 545 U.S. 844 (2005).