The nonsectarian or secular public school was the means of reconciling freedom in general with religious freedom. The sharp confinement of the public schools to secular education was a recognition of the need of a democratic society to educate its children, insofar as the State undertook to do so, in an atmosphere free from pressures in a realm in which pressures are most resisted and where conflicts are most easily and most bitterly engendered. Designed to serve as perhaps the most powerful agency for promoting cohesion among a heterogeneous democratic people, the public school must keep scrupulously free from entanglement in the strife of sects.

Felix Frankfurter (1882–1965) American jurist, teacher; US Supreme Court Justice (1939–62)

McCollum v. Board of Education 333 U.S. 216–217 (1948) [concurring]
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