I do not agree that Christ established the Catholic church. Maybe that's what the Pope teaches, but that doesn't make it true. God says to "Do" His Commandments. We are saved by Grace, but that does not mean we no longer have to obey Gods law.
John 14:15 “If you love Me, keep My commandments.
The term universal church was used at least since the second century. In any case, distinguishing the earlier church from the Catholic Church, aka the Roman Catholic Church, is a favorite pastime of many, especially since the Reformation and generally for the purpose of distinguishing
their particular theology from that of the big bad carnal Catholic Church. Some Protestants beginning 500 or so years ago, and then later, 150 or so years ago with the JWs, SDAs, and Mormons, all use many of the same arguments, from Scripture (even as the doctrine of Sola Scriptura opened the door to widespread differences among its own adherents) combined with often conveniently loose readings or pop-revisions of history and sometimes extra-biblical revelations. They just
know the right way as they valiantly strive to revive the true faith that was somehow lost for the last 1500-1850 years until
they exclusively and fortunately came along (except for the "remnant", of course, that some refer to even as as they identify that group differently).
We are saved by Grace, but that does not mean we no longer have to obey Gods law.
Amen. And it should be noted that the ancient churches are not even close to anti-nomianism as some Protestants are or tend towards being. In the EO and Catholic faith, for example, obedience of the commandments are necessary even if that obedience is now meant to come a new way, by the Spirit and not by our own efforts. But the Church knows that we still need to be cognizant of that obligation, so we still need to
hear the law in the form of the decalogue. If the church were to waffle about, say, the morality of murder, adultery, or theft, I might find your position a
bit more tenable at least. But the Church doesn't stop there; she explains and expands on the meaning and application of those commandments, knowing, for example, that abortion amounts to the taking of innocent human life as well and steadfastly taking a stand against it even as many non-Catholic Christian Churches fail to do so in modern times.
The change from Saturday to Sunday day of rest and worship (even though Saturday Sabbath is still practiced to some extent alongside of Sunday in some areas of the world) had its seeds at the beginnings of our faith when believers gathered and broke bread on the Lord's Day-with that practice continuing on as early fathers attest. Scripture, alone, cannot serve to inform us just how the Church is meant to be or how it should look today-that's all speculation and is nearly tantamount to believing that our own lives must follow a script, instead of playing itself out with whatever twists and turns life may have to offer. We don't call the shots, and God doesn't dance to anyone else's tune.