THE CLASHES BETWEEN competing rights that characterize the Bill of Rights in operation come into particularly sharp focus in the field of religious liberties. This is because the Bill of Rights expressly protects two very different forms of religious liberty which often are at odds with each other.

"Congress shall make no law respecting an establishment of religion," the First Amendment says, "or prohibiting the free exercise thereof." The purpose of the first clause, known as the Establishment Clause, is to prevent the government from setting up an official or government-favored religion. This clause has also come to stand for the separation of church and state—for the proposition that the government must not become too entangled in religion, even short of setting up an official religion. The second clause, the Free Exercise Clause, prohibits the government from interfering with individuals' right to...