The only Commandment not repeated in the New Testament, in the Age Of Grace:
“Remember the Sabbath day, to keep it holy”.
Anyhow, does it really matter? As long as the doctrine of soteriology is the foundation of the Christian, this focus on the day of the week seems very legalistic.
I think Sunday is the way to go, but others in my denomination have other ideas. Seventh Day Baptists began in the 1600s, and in my family’s neck of the woods there used to be a large contingent of them. (The reason Mom’s church is called “First Day Baptist”.)
Their belief of salvation is sound. They’re no less saved than those who worship on Sunday. You can be a person who doesn’t officially worship on any specific day, at any specific place, and be a Christian. Legalism can cloud and overshadow what’s important.
“The main thing is to keep the main thing the main thing”,i.e., salvation. (No, it’s not in the Bible.)
That may have been the same question Adam and Eve had over the apple. It seemed like a small thing.
It matters to God and that should mean something. That should carry weight. We all have to be accountable to God and IF He asks you why didn't you obey His Ten Commandments, what will your answer be? You know the verses "IF you love Me, keep my Commandments" and many others and the excuse may sound pretty lame on that great and fearsome day.
Whom does He tell "Depart from Me, I never knew you?" Atheists? No Agnostics? No These are people claiming, grace, miracles in His name and the right soteriology. They are completely shocked.