The Hosanna-Tabor case concerns the separation of church and state, an arrangement that is often misunderstood but is nevertheless a critical dimension of the freedom of religion protected by the First Amendment to our Constitution. For nearly a thousand years, the tradition of Western constitutionalism - the project of protecting political freedom by marking boundaries to the power of government - has been assisted by the principled commitment to religious liberty and to church-state separation, correctly understood. A community that respects - as ours does - both the importance of, and the distinction between, the spheres of political and religious authority is one in which the fundamental rights of all are more secure. A government that acknowledges this distinction, and the limits to its own reach, is one that will more consistently protect and vindicate the liberties of both individuals and institutions.
The “ministerial exception,” at issue in Hosanna-Tabor, is a clear and crucial implication of religious liberty, church autonomy, and the separation of church and state. Because any worthwhile account of religious freedom would respect the authority of religious communities to select freely their own clergy, ministers, teachers, and doctrines, any such account must include something like the ministerial-exception rule. Reasonably constructed and applied, this rule helps civil decision-makers to avoid deciding essentially religious questions. In addition, and more importantly, it protects the fundamental freedom of religious communities to educate and form their members. Although the exception may, in some cases, block lawsuits against religious institutions and communities for discrimination, it rests on the overriding and foundational premise that there are some questions the civil courts do not have the power to answer, some wrongs that a constitutional commitment to church-state separation puts beyond the law’s corrective reach. The civil authority - that is, the authority of a constitutional government - lacks “competence” to intervene in such questions, not so much because they lie beyond its technical or intellectual capacity, but because they lie beyond its jurisdiction.
Thomas C. Berg et. al., Religious Freedom, Church-State Separation, and the Ministerial Exception, 106 Nw. U.L. Rev. Colloquy 175 (2011)