Recently I became aware that in much of Europe, Monday is considered the first day of the week. That observation caused me to ask how anyone would know what day was the first day of the very first week or any week in antiquity.
This question is only relevant because a number of world religions base key aspects of their theology on knowing the first or maybe the seventh day of the week. If, in fact, it is important to God that certain religious activities take place on a certain numbered day of the week, then there should be some concrete way to tell whether the first day is Sunday or whatever.
How did we get a seven day week in the first place? Some would respond that God prescribed such in His sacred text. Actually though, historians tell us that the seven day week predates the Bible and Koran, both of which recount the seven days of creation with which we are so familiar. Even if the seven day week is divine in origin, that still does not answer the question as to which day in our current week is the first or last in God's eyes.
Just as years are arbitrarily numbered from some starting point, so too the days of the week have been counted down by seven from some arbitrary starting point. History records that the calendar has gone through a series of modifications or adjustments made necessary because of imprecise measurements of the length of a year. These alterations have almost certainly affected the number sequence of week days. Also, different calendars have been used by different cultural groups throughout human history. Whose calendar is the sacred one? We have no way of knowing what day of the week is first or last in relation to any theoretical first ever week.
Countless religious squabbles and separations have come about over the issue of which day is the proper one to engage in a religious activity. I conclude that such arguments are useless. If God is so particular about such things, we are left to guess what is right and hope for the best.
Sounds a lot like the theology of the average man- I'll do the best I can and leave the rest to God.