You wrote...
But as I pointed out already, these same people take their day of rest on Sunday, which is a practice put in place by the Catholic Church; there is no authority found in Scripture for this practice.
This is simply not true.
Early in the history of the Christian church,Christians had made the transition to worshiping on SUNDAY because of what Scripture revealed about practice of celebrating Sundays (Lord's Day) and because of the significance of other important events to Christianity that occurred on Sundays.
Among these events and practices:
Christ rose on the FIRST DAY (Sunday):
The Apostle Paul gave Christians instructions about setting aside money to giveJohn 20:1 - Now on the first day of the week Mary Magdalene came to the tomb early, while it was still dark, and saw that the stone had been taken away from the tomb.
1 Corinthians 16:1-2 ESV - Now concerning the collection for the saints: as I directed the churches of Galatia, so you also are to do. On the first day of every week, each of you is to put something aside and store it up, as he may prosper, so that there will be no collecting when I come.
Pentecost itself was on a Sunday
Christ was crucified on a Friday, was inside the tomb on the Passover Sabbath, and then rose on Sunday, beginning the count to the 50th day (Pentecost), which would be a Sunday. This 50th day was a Sunday, the very first day of the 8th week.
Christ fulfilled the Law, including the Sabbath (Saturday).
Matthew 5:17 -“Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them.
Finally, for my post, I note that out of the 10 commandments, only keeping the Sabbath (Saturday) is not repeated in the NT as a requirement for Christians.
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To argue that Christians today only worship on Sunday because Rome "proclaimed it" is not a convincing argument.
And while Christians are commanded to:
Hebrews 10:25 - "not forsaking our own assembling together, as is the habit of some, but encouraging one another; and all the more, as you see the day drawing near."
Christians are not commanded to specifically choose Sunday.
As such, no additional authority is ever needed.
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You also wrote the following...
We read as well in the New Testament how the Church, exercising its teaching authority in the form of the Magisterium (one of the other two pillars of authority) declares that circumcision is no longer necessary and that certain meats were no longer considered unclean.
Christians obey the Scriptures - all written by Apostles.
Today, every church has the spiritual gift of "teachers" given to the church. They are to be obeyed, so long as they do not violate Scripture.
There are however, no more Apostles, who were a foundation for the Church.
Consequently, I also find this argument of yours to be false.
In closing, I wish you every blessing in 2020.
May God reelect President Trump in a landslide.
You wrote...
But as I pointed out already, these same people take their day of rest on Sunday, which is a practice put in place by the Catholic Church; there is no authority found in Scripture for this practice.
This is simply not true.
But it is.
Despite the fact that the followers of Christ would gather to pray on Sunday, they still kept the Jewish Sabbath. (It's the reason they were getting thrown out of the synagogues.)
There's simply no instruction anywhere in the New Testament that allowed anyone to work on the Jewish Sabbath and to take their day of rest on Sunday; this was put into place by the Catholic Church.
It isn't just the Catholics who disagree with your interpretation of Scripture. Say what you will about the Seventh Day Adventists, but they are consistent about "Sola Scriptura". (They don't recognize the acts of the Magisterium in declaring foods to be clean or in declaring the day of rest to be the first and not the seventh day of the week.)