First Amendment

Bill of Rights
Amendment I

• 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 very first clause of the very first Amendment to the Constitution makes a firm, unequivocal statement.

It does not say "The government shall allow no religious content in any organization, building or event connected in any way with the government."

In fact, it does not say "The President shall make no rules respecting an establishment of religion." Note that our Constitution does not even prevent the creation of an Executive Branch bureaucracy to oversee and control religion (that would be scary!).

It says, in plainer language, "Congress cannot make a law that creates or defines a religion."

For religions NOT established by Congress (which means all of them!), it does not say anything about NOT allowing any religious displays or content provided by these religions.
Oops, my mistake
It does say something...

It says, in plainer language, "Congress cannot make a law prohibiting the free exercise of religion."

Can it be any clearer?