In one of his letters Thomas Jefferson remarked that in matters of religion "the maxim of civil government" should be reversed and we should rather say, "Divided we stand, united, we fall." In this remark Jefferson was setting forth with classic terseness an idea that has come to be regarded as essentially American: the separation of Church and State. This idea was not entirely new; it had some precedents in the writings of Spinoza, Locke, and the philosophers of the European Enlightenment. It was in the United States, however, that the principle was first given the force of law and gradually, in the course of two centuries, became a reality.
If the idea that religion and politics should be separated is relatively new, dating back a mere three hundred years, the idea that they are distinct dates back almost to the beginnings of Christianity. Christians are enjoined in their Scriptures to "render ... unto Caesar the things which are Caesar's and unto God the things which are God's." While opinions have differed as to the real meaning of this phrase, it has generally been interpreted as legitimizing a situation in which two institutions exist side by side, each with its own laws and chain of authority — one concerned with religion, called the Church, the other concerned with politics, called the State. And since they are two, they may be joined or separated, subordinate or independent, and conflicts may arise between them over questions of demarcation and jurisdiction.