Are you sure Sunday is the first day of the week?
Many cultures use Monday, most calendar software uses Monday, as well as retail.
Which system of day counting do you use?
Just curios as you are so adamant on the Sunday thing,
But aren't they all His?
Can anybody state with authority that today is Tuesday in the U.S.? I mean starting from day 1, going through the great flood and up to the present day, based on the earth's rotation, which by the way is not 24 hours exactly - and even the "leap year" system isn't absolutely accurate.
So we set aside one day in seven and honor our Lord and Saviour with a "Lord's Day".
Are you sure Sunday is the first day of the week?
But that argument is not even mentioned in the Churches concerning the change from Saturday to Sunday, the only argument the Church uses is that Jesus rose on the first day of the week and that Pentecost was on the first day of the week and the Apostle Paul taught on the first day of the week.
This is all in scripture, so the early Church being held on the first day of the week decided to call it the Christian Sabbath and then the Sabbath, they actually thought they could change the Sabbath, they were wrong.
What God did can not be changed, no more than the date of Custer,s last stand or some ones birthday.
We can Worship God or hold Church service any day of the week but we can not change the day God rested from his work.
If what you suggest was proved to be true then the Churches would have to keep awful quite about it or be in turmoil trying to start holding Church service on Monday,