Today we celebrate the 230th year of our nation's existence. John Adams thought that July 2 would be the date because the Declaration of Independence was adopted that day. The signing day, July 4, however, became the anniversary we remember.
The Constitution was adopted in 1791. The first ten amendments, the Bill of Rights, adopted December 15, 1791, were proposed to make ratification by the states more palatable. Among those rights we recall the first, granting freedom of religion (along with freedom of speech, of the press, of peaceable assembly, and to petition the government for redress of grievances). Actually it really is a prohibition against establishing a state church (the non-establishment clause).
While the Middle Ages are slandered with the accusation that there was a state church then, the facts of history prove that false. Of course, everyone was a Catholic (no heretics, Muslims, or Jews need apply) in those days. That's obvious. Nevertheless, the princes of the Middle Ages were constantly at loggerheads with the Church over its rights and theirs. The Church was independent of princes, an idea that was fought over for centuries with ambivalent success for both parties. (The illustration at left shows Gregory VII fleeing Rome and the troops of the German Emperor Henry IV---a conflict that had ambivalent outcomes.)
It is only with Luther and other reformers who needed the help of the princes that the divine right of kings becomes a Protestant idea. Without the help of the princes, and their desire to absorb the Church, the establishment of state churches would have been difficult, if done at all. The remnants of these state churches can be seen in the UK, the Netherlands, north Germany, and Scandinavia. Our founders sought to keep that idea out of our national arrangement. The Puritans had suffered from the Established Protestant Church, hence their move to New England. With the non-establishment clause, those who had suffered under state church affliction were assured that they would be free of it in the US. Many gladly went back to England in the 17th century to fight against Charles I, defeating him and establishing the Commonwealth under Oliver Cromwell.
Just to set the record straight, the legacy of non-establishment in the Bill of Rights is a reaction to Protestant state control of churches. The common perception of this is that we have freedom of religion, i.e., anything we call religion we are free to do. This is embodied in phrases like "we can worship any way that pleases us," or "worship at the church of your choice." This is all well and good in a nation of laws and protection of the minority. As Catholics, of course, we cannot abide this. We accept it (freedom of religion) because by the law of Christ there can be no coercion of conscience. We accept it because of the social contract, and we work to preserve it because it helps us. The last thing we would want is the Protestant hegemony taking church property and afflicting us. The whole phenomenon of Catholic parochial schools rests on the fact that the public school system of the 19th century was Protestant. Catholics were discriminated against, and evangelized in the public schools. Catholic education arose as a way of protesting that, although at most, there have never been much more than ten percent of the total of Catholic children in Catholic schools.
Getting back to the popular understanding of freedom of religion, we know that worship is not about us! It is about God. From a Christian understanding, we do not have the freedom to worship God as we want. We have the freedom to worship God as he wants. This is an important distinction. For all those lax Catholics who think the other way, it is necessary to ask ourselves at all times "What does God want me to do?" "What must I do to please God?" Aside from taking up the cross daily, when we come to worship, we worship in the way that he has established. I offer that this is the establishment clause that we should live under in our daily life as followers of Christ. To do any less is to abuse the freedom that we have in Christ, and while it is not the same as worshipping Baal, it comes very close to worshipping the self---in which there is no salvation.