In his opinion for the Court in the landmark case of Everson v. Board of Education, Justice Black held that the Establishment Clause of the First Amendment erected a high and impregnable "wall of separation" between church and state. Relying primarily on the writings of James Madison and Thomas Jefferson to discern the intentions of the framers, Justice Black maintained that, at the very least, the establishment proscription meant that
rn]either a state nor the Federal Government .. .can pass laws which aid one religion, aid all religions, or prefer one religion over another .... 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 form 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.
Ultimately, the Court developed a tripartite test, based on Everson's strict separationist standard, to apply in cases arising under the Establishment Clause. Formally proclaimed in the case of Lemon v. Kurtzman, that test stipulated that to comport with the establishment prohibition a governmental action must (1) have a secular purpose, (2) have "a principal or primary effect . . . that neither advances nor inhibits religion," and (3) "not foster an 'excessive government entanglement with religion."
Roald Y. Mykkeltvedt, Souring on Lemon: The Supreme Court's Establishment Clause Doctrine in Transition, 44 Mercer L. Rev. 881 (1993).