I beleve thats the law of God, Christ gave that law as the God of the OT and came and renewed it in NT yes Sabbath keeing is part of salvation as are all of Gods laws.
Now Sunday keeing in so called christianity started in Costantines time. he was a sun worshipper and brought it into the new Catholic church adopted to bring pagans into their fold along with many of our modern worlds doctrines
STUDY PEOPLE!
I could care less about Constantine or the council of nicea or lacodicea , the outlawing of Sabbath keeping was wrong, and should not have been done.
as my pastor says " Constantine was a lot more roman and empire than he was holy '
equally as wrong as saying that one has to keep the Sabbath to be saved
there are several references to Christ followers meeting on the first day of the week.
and when John said he was ' in the sprit on the Lord's day," he did NOT say Sabbath, a different greek word was used , not sabbaton,
and, God was very specific about when the Sabbath was to be kept.
so, unless you are 100% sure you are using the scared Hebrew calendar , you are not " keeping the Sabbath, '.
it strikes me as funny that you judeaizers ignore the fact that you were born on a day that is named after a pagan god, in a year of a Gregorian calendar, want to lecture us about going to church on the day of the sun, as if we are worshiping the sun god while we are praising Jesus.
we come to mt. Zion of the living God, you try to drag us back to Sinai, to the ministry of death, written on stone,