The "Religion Clauses" of the First Amendment of the US Constitution guarantee that the USA is a secular State, i.e. that there is separation of Church and State.

Click HERE to read JFK's 1960 speech: "I believe in an America in which separation between Church and State is Absolute"

First Amendment of the Constitution: "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."

The Establishment Clause is the first of the two "religion clauses" in the United States Constitution: "Congress shall make no law respecting an establishment of religion. . ." i.e. Congress cannot establish a national religion or favor any religion.

The Free Exercise Clause is the second of the two "religion clauses" in the United States Constitution:  "...or prohibiting the free exercise thereof " i.e. Congress cannot stop people from practicing a religion.