[identity profile] a-pawson.livejournal.com 2008-11-14 08:50 am (UTC)(link)
On the 7th day the Lord rested. The sabbath is indeed the last day of the week. But sabbath is a Hebrew word, and the Jewish sabbath is Saturday, hence why Sunday is the first day of the next week. Quite how Christianity came to decide Sunday was to be the sabbath I have no idea.

[identity profile] marrog.livejournal.com 2008-11-15 03:32 am (UTC)(link)
I think, possibly, as someone else suggested, they were confused by Easter.