The ISO 8601 was a man-made system to avoid confusion on the days of the week. If you go to the internet and find a site called "Etymology Dictionary", (http://www.etymonline.com/
) put in the search bar the words Saturday & Sunday. The results will say that Saturday is the seventh day, and Sunday is the first.
How then, did Sunday Worship come about?
The answer comes in two parts.
1. The name 'Thursday' comes from 'Thor's Day'. Each day has a history in its name. The name for Sunday came from the Sun Worship, created by Nimrod.
Quoting here from The Schaff-Herzog Encyclopedia of Religious Knowledge Vol. III, 1884, pp 2259-2260: "Sunday (dies solis of the Roman Calendar, 'day of the sun' because dedicated to the sun), the first day of the week was adopted by the Early Christians as a day of worship...it was called the 'Lord's Day'... No regulations for its observance are laid out in the New Testament, nor indeed its observance even enjoined..."
That quote shows that Sunday was ADOPTED by the Christians. Sunday, the day that was named after Sun Worship, was adopted.
2. In the early 300 AD's, Constantine became emperor of Rome. Constantine too had adopted Sun Worship. But there were still many people who worship God on Saturday, the seventh day. To settle the debate, Constantine, who had been a sun worshipper, issued the following decree: "On the venerable day of the sun [Sunday] let the magistrates and people residing in cities rest
, and let all workshops be closed.
According to the book, Lectures on the History of the Early Church
, by Dean Arthur P. Stanley p.291, Constantine did this as a way of "harmonising the discordant religions of the Empire under one common institution".
The original day was Saturday, but a man who was biased towards a certain day made the decision for everyone on what day HE thought was right. It's not up to man to decide what is right and wrong, rather it is God's decision.
Onto whether or not God's decision of the seventh day was 'arbitrary
' or not, that is beside the point. It may or may not have been random, but we will never know (unless He enlightens us), because as Isaiah 55:8-9 says, God's ways and thoughts are higher than ours.