Israel only was given the Sabbath. not the whole world.
Well the bible says "
The sabbath was made for man"
Isaiah 66:23 (KJV)
And it shall come to pass, that from one new moon to another,
and from one sabbath to another, shall all flesh come to worship before me,
saith the Lord.
and by the way, since the Sabbath was based on the sacred calendar, and we have been on the Gregorian calendar for about 431 years, are you 100% beyond a shadow of a doubt sure that you have the right day. it would be pretty insulting to God to claim to keep the Sabbath as laid out at Sinai, but really have the wrong day.
These people where sure about it, so am I sure of the right day of the week.
-Astronomy observence
"The human race never lost the septenary [seven day] sequence of week days and
that the Sabbath of these latter times comes down to us from Adam, though the ages,
without a single lapse."—Dr. Totten, professor of astronomy at Yale University.
"Seven has been the ancient and honored number among the nations of the earth.
They have measured their time by weeks from the beginning. The origin of this was
the Sabbath of God, as Moses has given the reasons for it in his writings."
—Dr. Lyman Coleman.
"By calculating the eclipses, it can be proven that no time has been lost and the
creation days were seven, divided into 24 hours each."—Dr. Hinkley,
The Watchman, July 1926 [Hinkley was a well-known astronomer].
"There has been no change in our calendar in past centuries that has affected in
any way the cycle of the week."—James Robertson, Director American Ephemeris,
Navy Department, U.S. Naval Observatory, Washington, D.C., March 12, 1932.
"It can be said with assurance that not a day has been lost since Creation, and all
the calendar changes notwithstanding, there has been no break in the weekly cycle."
—Dr. Frank Jeffries, Fellow of the Royal Astronomical Society and Research
Director of the Royal Observatory, Greenwich, England.
There is no question about which day the seventh day of the week is.
The weekly cycle
The break between the shift from the Julian to the Gregorian calendar?
There was a well known break of 10 days.
In 1582, that Thursday the 4th was followed by Friday the 15th.
The weekly cycle was not interrupted. Now take a look at 1752, Wednesday
the 2nd was followed by Thursday the 14th. Again, the calendar had to be
adjusted to correct it to the seasons but the weekly cycle remained unchanged.
The Origins of the Seven-Day Week, Eviatar Zerubavel
"Days, months, and years were given to us by nature, but we invented the week for ourselves.
There is nothing inevitable about a seven-day cycle, or about any other kind of week; it represents
an arbitrary rhythm imposed on our activities, unrelated to anything in the natural order.
But where the week exists—and there have been many cultures where it doesn't—it is so deeply
embeddedin our experience that we hardly ever question its rightness, or think of it as an artificial
convention; for most of us it is a matter of 'second nature.'