Ah. I think there's a historical dimension that you're missing, and a technical meaning of "establish". The phrasing in the First Amendment is this: "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof;..." To establish a religion, in the sense that's relevant to the First Amendment, is to designate it as official. The framers of the Constitution knew that the Church of England, or Anglicanism, was the established church of Great Britain: from the time of Elizabeth I, an Anglican archbishop anointed the new king or queen, British tax revenues helped support Anglican churches, and a man who wanted to go to a British university or take a job in the British government was required by law to swear to the 39 Articles and to be a regular churchgoer. In Elizabeth's day, Catholics had to practice their version of Christianity in secret, and were subject to legal penalties if they were caught. And the framers were also quite aware that Europe in the 17th century had been wracked by religious wars - not wars between Christians and non-Christians, but between Catholic Christians and Protestant Christians; a good case can be made for the Thirty Years' War (1618-1648) as the first world war, or at least the first pan-Western-European war, and the issues, at least on the surface, were religious. I think the framers were anxious to ensure that the European religious disagreements weren't going to ravage the infant United States as well.