Why doesn't the Church keep the Bible Sabbath?

Which Church? I'm a Seventh-day Adventist, so of course we observe the 7th day along with the Creator, but many of the fervent Sunday churches teach the real Sabbath as well. Their serious people "rest" from Friday sundown to Saturday sundown according to the commandment, and then come together for celebration on Sunday. (I feel so fine after a good Sabbath rest, I feel like celebrating on Sunday, too!)