And so I say to you, you are Peter, and upon this rock I will build my church, and the gates of the netherworld shall not prevail against it. I will give you the keys to the kingdom of heaven. Whatever you bind on earth shall be bound in heaven; and whatever you loose on earth shall be loosed in heaven."As wbarmy pointed out, this was the practice in the second century and 1 Cor. 16:2 shows that the Christian church even under Paul was gathering on Sunday, the first day of the week, rather than on Saturday, the seventh:
Matt.16:18,19
Now in regard to the collection for the holy ones, you also should do as I ordered the churches of Galatia. On the first day of the week each of you should set aside and save whatever one can afford, so that collections will not be going on when I come.
1 Cor. 16:1,2
Worship and/or assembly on any particular day of the week isn’t an issue; therefore, worship and/or assembly on any or every day is fine. What’s in dispute here is observance of the 7th day as a sabbath rest. The fact that early believers met on “the first [day] of the week [sabbaton = sabbath or week)” does nothing to change the commandment, and scripture in no way indicates that early believers changed their sabbath observance. In fact, Paul continued to be Torah observant throughout his ministry.