Act 15:21 For Moses has had throughout many generations those who preach him in every city, being read in the synagogues every Sabbath."
Indeed, notice what the text states, that Moses was being read in the synagogues every Sabbath - not the churches which are shown coming together to break break upon the beginning of the 1st day, and having service then. (Acts 20:7) And considering the cardinal importance that you see sabbath keeping having, it is incongruous that this command be not manifestly affirmed under the new covenant.
Indeed, your entire post utterly fails to provide what is desperately needed, that of any reiteration or repetition of the 4th commandment under the new covenant, yet the other 9 are, while the only teaching under the new covenant is that which refers to the sabbath or sabbath days being a shadow of things to come, (Col 2:16) a rest which typifies what believers gain by faith, )Heb. 4) or any record of the disciples specifically having meetings on the 7th day, while they specifically met more than once on the 1st day, as shown.
Do you believe all those who do not keep the 7th day commandment, once told, are lost?
Yes, I am quite aware of what the texts state but obviously you are not.
Act 13:42 So when the Jews went out of the synagogue, the Gentiles begged that these words might be preached to them the next Sabbath. ... 44 On the next Sabbath almost the whole city came together to hear the word of God.
Where were the Gentiles? In the synagogue. Who came together the next Sabbath? The nearly the entire city, both Jew & Gentile, together in the synagogue. But what I find interesting is that you refer to the 4th commandment under the new covenant because based on the Prophets whom Jesus told us to heed, it is obvious that you have not spent much time in Isaiah regarding the place of Gentiles even though Jesus quite often quoted from Isaiah.
Isa 56:1 Thus says the LORD: "Keep justice, and do righteousness, For My salvation is about to come, And My righteousness to be revealed. 2 Blessed is the man who does this, And the son of man who lays hold on it; Who keeps from defiling the Sabbath, And keeps his hand from doing any evil." 3 Do not let the son of the foreigner Who has joined himself to the LORD Speak, saying, "The LORD has utterly separated me from His people"; ... :6 "Also the sons of the foreigner Who join themselves to the LORD, to serve Him, And to love the name of the LORD, to be His servants— Everyone who keeps from defiling the Sabbath, And holds fast My covenant—7 Even them I will bring to My holy mountain, And make them joyful in My house of prayer. Their burnt offerings and their sacrifices Will be accepted on My altar; For My house shall be called a house of prayer for all nations." 8 The Lord GOD, who gathers the outcasts of Israel, says, "Yet I will gather to him Others besides those who are gathered to him."
So according to the Word of God spoken through Isaiah, under the Messiah, the Sabbath still remains for all, including the Gentiles. Is this not what Paul told us in Heb 4? Why I do believe so. Sorry, but while you debate religion, I prefer to actually just quote Scripture and let the Word of Goid speak for Himself and here is how He defines the 'new' covenant:
Heb 8:8 Because finding fault with them, He says: "BEHOLD, THE DAYS ARE COMING, SAYS THE LORD, WHEN I WILL MAKE A NEW COVENANT WITH THE HOUSE OF ISRAEL AND WITH THE HOUSE OF JUDAH—9 NOT ACCORDING TO THE COVENANT THAT I MADE WITH THEIR FATHERS IN THE DAY WHEN I TOOK THEM BY THE HAND TO LEAD THEM OUT OF THE LAND OF EGYPT; BECAUSE THEY DID NOT CONTINUE IN MY COVENANT, AND I DISREGARDED THEM, SAYS THE LORD. 10 FOR THIS IS THE COVENANT THAT I WILL MAKE WITH THE HOUSE OF ISRAEL AFTER THOSE DAYS, SAYS THE LORD: I WILL PUT MY LAWS IN THEIR MIND AND WRITE THEM ON THEIR HEARTS; AND I WILL BE THEIR GOD, AND THEY SHALL BE MY PEOPLE. 11 NONE OF THEM SHALL TEACH HIS NEIGHBOR, AND NONE HIS BROTHER, SAYING, 'KNOW THE LORD,' FOR ALL SHALL KNOW ME, FROM THE LEAST OF THEM TO THE GREATEST OF THEM. 12 FOR I WILL BE MERCIFUL TO THEIR UNRIGHTEOUSNESS, AND THEIR SINS AND THEIR LAWLESS DEEDS I WILL REMEMBER NO MORE."
And of course we know that Paul is quoting Jeremiah 31:34. The covenant is not really new as the substance of it remains the same, the only difference is that through Messiah, all will know the Law because it will be in their hearts forever and ever and no one will need to be taught because all will know and do.
So I ask you, has this happened yet? Has what you call the 'new' covenant been fulfilled? Does everyone know the Law of God given to Israel and are is everyone in obedience to it as Jesus walked in obedience to it? You know, Peter said that we are "a chosen generation, a royal priesthood, a holy nation, His own special people". No where is the word 'church' used here. However the words 'nation', priesthood' and 'special' people are. So where did Peter get this from?
Exo 19:5 Now therefore, if you will indeed obey My voice and keep My covenant, then you shall be a special treasure to Me above all people; for all the earth is Mine. 6 And you shall be to Me a kingdom of priests and a holy nation.'
Words spoken to a mixed multitude that included Caleb, a gentile, a representation of the wild branch who joined himself to the natural branch, Israel and thus became a fellow citizen and member of God's house, His nation called Israel just as Paul says we do in Eph 2. No, there is nothing all together new, there is simply all that has been true from the beginning.
That is asking me to judge and that is not a command given to us. But what was given to us was to speak no deceit and so the truth is, He gave us His Sabbath, it is the 'sign' of His people whether Jew or Gentile. Our Messiah is the Lord of the seventh day Sabbath, the day in which He actually resurrected, so from here, the decision is up to those who read this. To study it out for themselves, to show themselves approved by working our their own salvation. Messiah came to redeem us from lawlessness, not to form new laws according to doctrines and traditions that had been in place my pagan religions for centuries before Messiah, the Word of God, came in the flesh.
Tit 2:14 who gave Himself for us, that He might redeem us from every lawless deed and purify for Himself His own special people, zealous for good works. 15 Speak these things, exhort, and rebuke with all authority. Let no one despise you.
The Word of God put in flesh, the Word of God walked in the flesh as an example of how we are to walk in the flesh. The Word of God was crucified, died and was buried and on the 3rd day, His Sabbath, the Word of God resurrected in newness of life. The only Word of God that existed at the time was that which is found left of Matthew that put on flesh just as the Word of God told us in Lk 24 and that Word of God is Moses, the Prophets and the Psalms. The same Word of God that Timothy had known from his childhood that ...
2Ti 3:15 and that from childhood you have known the Holy Scriptures, which are able to make you wise for salvation through faith which is in Christ Jesus. 16 All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, 17 that the man of God may be complete, thoroughly equipped for every good work.
Paul was not speaking of any Scripture that did not exist in Scripture form when he taught & preached. Paul was speaking of the only Word of God known to them and that was their Hebrew Scriptures that the church renamed the 'old' testament in order to profit from their false doctrine and invisible 'new' covenant that is no where to be found anywhere in any of the words of the Word of God, even when He was with us in the flesh.