For Christians, we now worship the Lord on the FIRST day of the New covenant
On whose authority? Where is the command from God? Who told you to worship on that day instead of the Sabbath? Tell me o clever one. Don't tell me He arose on the first day to honor Him. He plainly stated "IF you love Me, keep My Commandments".
On whose authority do Christians worship the Lord on the FIRST day of the New covenant?
On the authority of God.
God rose on the 1st day of the week to signify a New covenant.
If you do not do that, then you are one of those fallen away against whom the apostles were commanded to oppose.
Sabbatarians are not Christ followers
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.)