As Gal 3 points out - the first covenant has the terms: "obey and live". We see it in Genesis 2 and we see it "at the nation level -- not the individual level - in Ex 19 and 20.
By contrast the New Covenant is the one Gospel Gal 1:6-9, "preached to Abraham" Gal 3:8 and given to Adam in Gen 3. It is superior in that it provides salvation for the lost - but the Gen 2 condition did not.
reread that chapter 3 from Galatians
7 Understand, then, that those who have faith are children of Abraham. 8 Scripture foresaw that God would justify the Gentiles by faith, and announced the gospel in advance to Abraham: “All nations will be blessed through you.” 9 So those who rely on faith are blessed along with Abraham, the man of faith.
10 For all who rely on the works of the law are under a curse, as it is written: “Cursed is everyone who does not continue to do everything written in the Book of the Law.” 11
Clearly no one who relies on the law is justified before God, because “the righteous will live by faith.” 12 The law is not based on faith; on the contrary, it says, “The person who does these things will live by them.” 13 Christ redeemed us from the curse of the law by becoming a curse for us, for it is written: “Cursed is everyone who is hung on a pole.” 14 He redeemed us in order that the blessing given to Abraham might come to the Gentiles through Christ Jesus, so that by faith we might receive the promise of the Spirit.
All with faith are metaphorically "children of Abraham. But certainly not bound by "works of the law". What would be the point of freeing gentiles from circumcision, the initiation to the law, if they were going to be required to keep other commandments articulated in the law such as the weekly ceremony of Sabbath?
Obviously that does not man gentile Christians are free to murder they have instruction and guidance to not do such things out of love, not because of Torah and its capstone, the 10 Commandments.
And, of course, there is nothing wrong with a gentile keeping Sabbath as long as it is not kept as a work of the law, but rather as a personal act of piety.
Eve though Galatians 5
4 You who are trying to be justified by the law have been alienated from Christ; you have fallen away from grace.
Again from Galatians 3
24 So the law was our guardian until Christ came that we might be justified by faith. 25 Now that this faith has come, we are no longer under a guardian.