Where is that written? There is only one 7th day in a week….look on the calendar…it’s what corresponds to our Saturday.
There is no command to observe a Sabbath at all for Gentile Christians as the law was only given to Israel.
Jesus was Jewish and under law so he observed the Sabbath until the time came for him to sacrifice his life. With his death, a new covenant was established with the law now fulfilled in him and nailed to his torture stake with him as finished.
Col 2:13-17…ESV…
“And you, who were dead in your trespasses and the uncircumcision of your flesh, God made alive together with him, having forgiven us all our trespasses, by canceling the record of debt that stood against us with its legal demands. This he set aside, nailing it to the cross. He disarmed the rulers and authorities and put them to open shame, by triumphing over them in him. Therefore let no one pass judgment on you in questions of food and drink, or with regard to a festival or a new moon or a Sabbath. These are a shadow of the things to come, but the substance belongs to Christ.”
For Gentiles even their uncircumcised state was no longer a problem, because faith in Christ as Messiah covered their sins as well, giving them the hope of everlasting life.
No Jewish festival or observance was mandated for Gentiles.….as Paul clearly stated.
The original Phrygian population of Colossae were Greek and Jewish elements. The early Phrygians displayed a strong tendency toward spiritistic fanaticism, the Greeks indulged in much speculation and in philosophical arguments, and the Jews were advocates of the Mosaic Law and its dietary and sabbath requirements. All these attitudes were dealt with in Paul’s counsel to the Colossian congregation.
There is no sabbath mandated for Christians, so moving the “sabbath” to another day did not change God’s law…..the Roman Catholic church was formed as a fusion between Roman sun worship and weakened Christianity, so anything made into a “doctrine” by them was hardly spiritually clean. The Romans already dedicated Sunday as the day they honored their sun god. They deceptively snuck it in on the people to secure the place of Roman Catholicism as the “State religion” of the Empire……a religion that seemed to satisfy both elements of the Roman Empire….so called “Christians” as well as the pagans, merging them into one happy deluded family….so that no one had to give up what they loved…..the trouble was, God didn’t love any of it.