Separation of Church and State
Most people connect this phrase to the language of the Bill of Rights that guarantees no establishment of an official religion, and the free exercise of religion.
Through much of the late 20th century the idea was associated with the effort of atheists to eliminate prayer in schools, and with the effort of conservative Christians to exclude the theory of evolution from the classroom (or to include Creationism). The civil rights struggles of blacks, women, and gays also often turned on the question of the role of religious belief in the secular State. The entry of conservative Evangelicals into active politics in the late 1970’s and 1980’s with the creation of the Moral Majority by Rev. Jerry Falwell aimed at pushing back societal/cultural changes (including the exclusion of organized prayer in schools) seen as contrary to the Christian values of most Americans. At that point the separation of church and state increasingly became the cry of liberals/progressives (including liberal Christians and Jews) and secular voices, emphasizing the need for protecting the workings of the state and general public against the intrusion of religious groups/institutions seen as trying to force their religious views on the nation through the force of law. For religious conservatives, this effort has become seen as an attempt to push religious voices out of the public sphere entirely. While acknowledging a proper boundary between church and state, they argue that it was never intended by the Founders to exclude or silence these religious voices. These same people also emphasize that this doctrine was intended to likewise protect religions from the intrusion of the state.
This argument underlies the intense efforts to resist the imposition of requirements on organizations and people to financially or otherwise support activity they believe is contrary to their religion’s teachings, e.g. contraception, and same-sex marriage.