The Establishment Clause does not allow the government to support one religion more than any other religion. The government also can not say that a religion or a god is true. This is often described as "separation of church and state", where "state" means "The Government". It also does not allow the government to establish a national religion. It allows people to debate religion freely without the federal government of the United States getting involved. The clause did not stop the various states from supporting a particular religion, and several states did.
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances..