Congress can't make an official state religion, nor can they impede you from practicing your chosen religion. If you have one. Just like a Baptist has no right to force his belief on a Methodist, an Atheist has no right to force his belief (or lack) on someone who does believe. This has been the most common outcome, an interpretation favoring freedom FROM religion, not OF religion.
If the government is binding THEIR interpretation of scripture, IE -- Sunday is a day of rest, then they are in fact establishing a religion. They are also wrong doctrinally, since the "sabbath" is SATURDAY under the old Law, a law Christians are no longer bound by (see the entire book of Galatians). The New Testament church met on the first day of the week, SUNDAY, with no prohibitions for work, hunting, or other activity. Only nine of the 10 commandments are repeated in the NEW Testament. Keeping the sabbath is not one of them, meaning it is relegated to the Law of Moses.
To my Jewish friends I say this: I am perfectly accepting and respectful of your religious objections toward helping me fill feeders on Saturday.
I am likewise respectful of my Christian friends that have a similar objection for Sunday activity.
I am NOT respectful of any governmental attempt to bind me to either position. Such proclamations from on high are in response to the religious interpretations of lobbying groups that I very likely disagree with, and such errant views IMO should never be bound on the public, especially on those that do not hold those same views. Such impositions were the very foundation of our separation from a tyrant king.
This is why the government is a poor place to allow the imposition of faith. They and those that lobby them are not theologians that I trust to apply ANY doctrine accurately, and even if they were, doing so would clearly violate the first amendment. I'll take care of the application of religious doctrine within the walls of my own home, thank you very much.