Article 1 of the Bill of Rights clearly states the following: "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof ... ."
The first part of this statement has been construed to mean that there must be a separation of church and state in the United States and the second part permits the free exercise of religion. Today, we see the first part enlarged to the extent of saying that the "free exercise thereof" must be curtailed so that the first part of Article 1 may be satisfied.
This has effectively stopped the free exercise thereof. Christians may not freely celebrate Christmas in schools or any other public places even if those who wish to be exempted from it are permitted to exclude themselves.
We are not allowed to display nativity scenes on public property even though that property belongs to all of us in common trust.
There are some who do not want us to even have the right to practice the cornerstone of our religious beliefs (the birth and life of Christ) in any public forum, a right which the Constitution (Article 1 of the Bill of Rights) clearly states we do have.