Sorry but long posts require long responses...please read slowly
The issue of Exodus 16…We see in Exodus 12:2 that for His names sake in Israel, God made a brand new calendar….this for them was to be the beginning of months and that day was the 1ST day of the 1st month…and from that day forward the children of Israel were to follow a calendar not known to the rest of the world, nor even to them hithertofore….from that very chapter on we begin to hear about Sabbaths (says which the Lord had determined to set apart for His purpose and devotion to Him among these people and only these people)….Yes it is part of the covenant agreement with these people (never was insisted on for any other people)…
In Deuteronomy 5 when Moses is reiterating the terms of the covenant (which contains the 4th commandment) the Spirit through Moses shows us that these terms have never been covenanted with any other, not even their own fathers (Noah, Shem, Abraham, Isaac, or even Jacob)…none before these people were bound to keep this agreement. Though some were aware of this because of the story of creation, none were bound nor commanded to “keep the Sabbath” prior to this. The Israelites however were bound to keep all these 10 commandments and the feasts of Passover, and Unleavened Bread (the Passover on the 14th of Nisan, the first day of UB on the 15th and the last day of UB on the 21st were also days of Holy Convocation and Rest) perpetually for all their generations once they entered the covenant at Horeb.
The word Sabbath first appears in Exodus and is not anywhere found in the book of Genesis. Therefore the passage about the 7th day when God rested has no significance regarding a day someone is to keep until Exodus….we are made in His image and should have a day of rest because He foreknew as a result of the fall man would have to work by the sweat of his brow just to eat….it only became a Holy Ordinance for Israel to “keep it” in Exodus.
It is a day blessed by God…Yes indeed it is and I am blessed by it though I attend church (gathering for corporate worship) on the 1st day (after the order of the feast of first fruits upon which He rose overcoming death for our justification, the day He the new hope the eternal rest appeared to His disciples, and the day the Holy Spirit or new eternal life was birthed into those who faithed) and as you pointed out, history shows the early members of His body (because most were either Israelites or proselytes) gathered on the 7th day Sabbath (though nowhere commanded of God in the OT or the NT) and on the 1st or 8th day (we see this even in some of the earliest church writings)…
Jesus and the Apostles did this “as was His custom”, Paul also did this “as was his custom” they also kept the feast of dedication (Hannukah) and wore the tallith as was there custom. A “custom” is a tradition not based on a commandment from God but on the practice developed by the people and as taught by their religious leaders. None of these things are binding on Gentiles (Acts 15:5-20).
The practice of gathering together for corporate worship on the 7th day was a tradition developed during the Babylonian Captivity so people would not forget the Lord or His ordinances and continued when the children of Judah (the first Jews) returned to the land. There is no commandment to do this and nowhere in the OT do the children of Israel (with whom was the very covenant we are discussing) ever do this (gather on the 7th day for corporate worship at the Tabernacle or Temple) both Exodus and Leviticus make it perfectly clear that the Sabbath convocation and rest was to take place in the home and you were not to go far from your place on the 7th day…
Exodus 16:29 tells us “…abide ye every man in his place, let no man go out of his place on the seventh day.”
Leviticus 23:3 says “Six days shall work be done; but on the seventh day is a Sabbath of solemn rest, a holy convocation; ye shall do no manner of work; it is a Sabbath unto the LORD in all your dwellings. “
Note these important things…it is “a” Sabbath not “the” Sabbath. Also note “in” (inside of or within) “all” (many, plural) “your” (personal as in each one) “dwellings” (plural as in their homes)…
So having clarified that for the purpose of discussion when we read in the Holy Spirits theopneustos graphae that it is not about a day but about our devotional time and our need for a day of rest then it matters not which day we gather for corporate worship so doing so on the 7th day Sabbath is fine (if that is the tradition you wish to observe) but so is it also fine (in fact more in line with the Torah’s restriction on the Sabbath) to gather together for corporate worship on the 1st day (or 8th day)…
But the OP question was really HOW does one keep the Sabbath not WHY…
In His love
Brother Paul