This misunderstanding is probably where the idea that Monday is the first day of the week came from. Biblically, Saturday is the Sabbath, the last day of the week. But early Christians came together before and after work on the first day of the week, the day Jesus rose from the dead, which is explicitly the day after tue Sabbath. Eventually that day was also made a free day amd added to the weekend. But it was always the first day of the week until ISO redefined it.

If you’re interested… the reason Christians worship on Sunday is because Jesus was raised from the dead on the first day of the week. It wasn’t an immediate thing as at first almost all Christians were Jewish and continued the seventh day day of rest and gathering for worship.

No, the biblical day of rest is the Sabbath, the Saturday. The fact that most Christians keep the first day of the week instead of the last day is because Jesus rose from death on the first day of the week.

Yet the word "Sabbath" refers to different things to different Christians.

Consider the old nursery rhyme, Monday's Child, which ends with

Friday's child is loving and giving / Saturday's child works hard for a living. / And the child born on the Sabbath day Is bonny and blithe, good and gay.

I'm not familiar with that nursery rhyme, but it sounds like it's based on the same misunderstanding that lead to ISO 8601.

I’m actually really interested in this. Clearly in Jesus’s time the Hebrew week went Sunday–Saturday. That definition remained at least for long enough to make into Ecclesiastical Latin and further into, e.g., Portuguese (segunda-feira, etc.). So why does ISO 8601 go Monday–Sunday? Was it codifying existing practice in Europe? When did that practice begin? Was America colonized before Europe switched to Monday–Sunday, or is America’s Sunday–Saturday a fundamentalist reversion to something more Biblically accurate?

I live in Europe and I never learned anything other than that Sunday is the first day of the week. It's only very recently that I'm starting to notice an insistence that Monday is the first day. From my perspective, ISO 8601 seems to be the cause of that, and having an ISO standard on your side is certainly strengthening that position, but I think it's simply wrong.

Of course ISO 8601 didn't just drop out of thin air, but what caused it? I think it's a misunderstanding mixed with ignorance. Ignorance of the fact that the Jewish Sabbath, referred to everywhere in the Bible, is on Saturday, combined with people reading in the Ten Commandments about observing the Sabbath on the last day of the week and associating that with their own church attendance on Sunday, which they then conclude must be the last day of the week.

A more thorough reading of the Bible would have set them straight, as would some knowledge about history or other religions.

I actually used to think that Monday as the first day of the week was just a corporate thing. I first noticed it when I started working and work agendas were surprisingly insistent on starting on Monday. But I figured that was because the weekend is meaningless to the work week, so why not just lump it all together at the end? And then I learned about ISO 8601 and was completely flabbergasted that this was an official standard.

Another commenter posted a source that mentions in passing that ISO 8601 was the result of a 1978 UN declaration that Monday should be the first day of the week. Now I wonder where that came from!

I think it's a bit simplistic to call it a "misunderstanding." There are large swaths of Christianity that refer to Sunday as the Sabbath.

https://en.wikipedia.org/wiki/Sabbath#Christianity

You’re not wrong that “the Sabbath day” has sometimes been used by Christians to refer to Sunday, but the context of this thread is that a comment claimed that calling Sunday the first day of the week is inconsistent with the Bible, and that’s plainly not true.

> From a Christian point of view, it would make sense that Sunday is the last day of the week, as it is the official day of rest.

Depends on the Christian. If you mean the Puritans, from whom present-day prescriptions (such as no or limited alcohol sales on Sunday) derive, you may be on to something. If you mean the Sabbatarians, no doubt they have an explanation, but I don't know it. If you mean a Seventh-Day Adventist, you'd be wrong, because they still hold to Saturday as the seventh-day and the sabbath. If you mean a Catholic or one from another denomination, the Catholic catechism teaches that Sunday is the fulfillment of the spiritual truth of the Jewish sabbath, and most other denominations understand similarly.

Well, yeah, the Sabbath should be Saturday. That doesn't mean we can't have Sunday be the day we go to church.