The debate on the Sabbath day is a good illustration of some of the key theological differences between the old and new covenants (testaments).
In the Old Testament, God stated, "Remember the Sabbath day to keep it holy….” It was the custom of the Jews to come together on the Sabbath, which is Saturday, cease work, and worship God. Jesus went to the synagogue on Saturday to teach, as did Paul. So why do Christians worship on Sunday?
First of all, of the 10 commandments listed in Exodus 20:1-17, only 9 of them were restated in the New Testament. The one that was not reaffirmed was the one about the Sabbath. Instead, Jesus said that HE is the Lord of the Sabbath (Matt. 12:8).
In creation, God rested on the seventh day. But, since God is all-powerful, He doesn’t get tired. He doesn’t need to take a break and rest. So, why did does it say that He rested? The reason is simple: Mark 2:27 says, "The Sabbath was made for man, and not man for the Sabbath." In other words, God established the Sabbath as a rest for His people, not because He needed a break.
The OT system of Law required keeping the Sabbath as part of the overall moral, legal, and sacrificial system by which the Jewish people satisfied God’s requirements. The Sabbath was part of the Law in that sense.
But with Jesus’ atonement, the requirements of the Law were fulfilled in Christ. We now have rest from the Law. We now have "Sabbath", continually. So Tiassa, Christians are not violating their law.
The Seventh Day Adventists have every right to worship on the Sabbath and they should if they are convinced that is the right thing to do. However, if any member of any church were to require a person to worship on the Sabbath as a sign of "true" Christianity or "true" redemption, then that would be wrong.
Sunday as a day of worship is seen in Acts and a few other places and slowly became tradition. The idea of Sunday being “The Lord’s Day” came about in the second century. But Christians are free to worship any day they please.