So, when it comes to freedom of belief systems and freedom of cultural expression, you can talk about it, you can write about it in the newspaper, you can get together with others to discuss it, and you can write to the government to complain about it. But if you do it, you are on your own without Constitutional protection.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.
In religious matters, you can do all this and in addition you can "exercise" your beliefs, rituals and conventions freely.
Documents are written in particular places and times. Many articles of the U.S. Constitution show what the Founding Fathers were most afraid of. Evidently number 1 on the list -- the very first words of the Bill of Rights -- was that future sessions of Congress might pass a law establishing a state religion, force everyone to join, and punish people who didn't.
Two and a quarter centuries later, the course of the American Republic has been such that this danger has receded. Still, you never know. Just when you let your guard down they might start requiring all school children to chant in unison, "one nation under God..."
It has required repeated rulings by the U.S. Supreme Court, sitting as arbiters of the Constitution, to make sure that local school boards and other governmental and quasi-governmental agencies do not require people to say the Pledge of Allegiance. Interestingly, these cases have mostly been brought not by atheists who don't want to praise God, but by religious groups who object to pledging allegiance to anyone but God -- in particular, not to the federal government.