Then feel free to explain exactly why gov't doesn't work on a sunday, since you just crossed out these two options
The US government used to deliver mail on Sundays; they wisely heeded the First Amendment. Starting in 1820, Protestant ministers started demanding that the US stop deliveries, for two reasons. One (the most often stated reason) was that it was unholy. It was "part of the churches’ wider efforts to enforce a 'Puritan Sabbath' against the demands of Mammon [the devil.]" The second reason was more mundane; people would congregate in the post office whenever the mail came in to pick up their mail, and since everyone was there, it turned into a social event, with people playing cards and gossiping. This, of course, resulted in fewer people going to church - and thus fewer contributions.
However, for a while, the government resisted the calls to make Sunday a Christian holiday. In 1828, Kentucky Senator Richard M. Johnson (war hero and devout Baptist) stated that any federal attempt to give preference to the Christian Sabbath would be unconstitutional. He noted that religious intolerance had both led to people coming to the US, and to a war of independence, and thus the US had drawn a line between government and religion. In fact, he stated that ”the line cannot be too strongly drawn." So they failed - for a while.
Finally, though, the religious leaders found an ally - the labor unions. The unions wanted a plausible excuse for a day off, and so they, along with the ministers, pressured the government to close the post offices on Sunday. The law was passed in 1912, in contradiction to the First Amendment. Other government offices followed suit, since in the early days of the US, nothing could be done without the mail.
For over a century, the Christian Sabbath has thus been officially observed by the US government. Fortunately that is now changing, and some areas now offer Sunday mail delivery.