The First Amendment of the United States Constitution protects the right to freedom of religion and freedom of expression from government interference. See U.S. Const. amend. I. Freedom of expression consists of the rights to freedom of speech, press, assembly and to petition the government for a redress of grievances, and the implied rights of association and belief. The Supreme Court interprets the extent of the protection afforded to these rights. The First Amendment has been interpreted by the Court as applying to the entire federal government even though it is only expressly applicable to Congress. Furthermore, the Court has interpreted, the due process clause of the Fourteenth Amendment as protecting the rights in the First Amendment from interference by state governments. See U.S. Const. amend. XIV.
Two clauses in the First Amendment guarantee freedom of religion. The establishment clause prohibits the government from passing legislation to establish an official religion or preferring one religion over another. It enforces the "separation of church and state." Some governmental activity related to religion has been declared constitutional by the Supreme Court. For example, providing bus transportation for parochial school students and the enforcement of "blue laws" is not prohibited. The free exercise clause prohibits the government, in most instances, from interfering with a person's practice of their religion.
http://www.law.cornell.edu/wex/First_amendment
Freedom OF religion, not Freedom FROM religion. The United States and the Constitution were based on a belief in God.
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