The Sabbath is a Jewish word and is Saturday.
Sunday was the day that Christians started to meet after the Resurrection. It is not the Sabbath. Anyone who refers to Sunday worship as a Sabbath is distorting scripture and there is a fatal judgement for that from Christ.
7th Day Adventists meet to worship on Saturday. They also distort scripture to do that, but they are typically decent people, if not saved. Some are, as in all Christian faiths.
Denominationalism is twist by man to make themselves more holy. Doesn't work at all. Only seems to separate further.
The Church that Christ, Peter, John, Jude, James and Paul refer to is the body of real believers that Christ will come for in the Rapture, which is very close.
Most think they are saved, but there was no transformation. They will get another chance after the Rapture, after they change their drawers.
This sad fact is the saddest thing I know as a believer for 33 years. I pray for the lost all the time.
Most don't think they are lost. But they are.
Real faith erupts from a believer in thought and deed and worship. Few do that in the world without trying to make it into a form of works faith.
Works faith is dead and so are its adherents.
But they won't face their sin.
That is the first step. Second is that sin separates us from God in Christ.
And so on.