When did God authorize a change in the Sabbath from Saturday to Sunday? This is the usual phrasing of a question about the difference between Sabbatarians (Seventh Day Adventists, Seventh Day Baptists, Church of God-Sabbatarian, and smaller groups) and other Christian groups. It goes directly to the doctrine that most distinguishes them from other denominations. (I speak here primarily of "Seventh Day" Sabbatarians, not the few "First Day" Sabbatarians.)
Most Sabbatarians are at least consistent in that they also follow other aspects of the Law of Moses, most notably the dietary laws, in addition to keeping Sabbath. Some keep kosher by modern Orthodox Jewish practice, while others keep the letter of the Law without the rabbinic decrees of keeping kosher. Some however, do not keep God's appointed feasts on the dates specified in Leviticus 23, or fail to follow other commands of the Law.
Those who ask that question that started the first paragraph, including many from these groups, reveal a fundamental misunderstanding of the Sabbath, and of the non-Jewish Christian's responsibility toward the law.
How does this question reveal a misunderstanding of the Sabbath? Sunday is not, and never has been the equivalent of the Sabbath for Christians. Most Sabbatarians keep Sabbath by refraining from normal workday activities, as would be proper. But to say what we do on Sunday is "keeping Sabbath" is far from accurate. Under the Law of Moses the Sabbath is a day of rest from creative work, but nowhere was it ever a set aside day for congregational assemblies or for worship. Throughout most of Jewish history it has been kept more in the home than in the synagogue. Christians assemble on Sunday as they have been doing since the early days of the church (Acts 20:7; 1 Cor 16:1-2) but they are not attempting to keep Sabbath.
Are non-Jewish Christians obligated to keep any part of the Law of Moses (including the Ten Commandments)? If so, to what extent? This is the heart of the difference between Sabbatarians and other Christians.
While the book of Galatians may address this issue, the principal passage that deals with it is Acts 15. Certain Jewish Christians were saying that Gentiles must be circumcised and keep the Law of Moses. The question was referred to the elders and apostles in Jerusalem. Under the influence of the apostle Peter and the elder James, both Jews, a letter was published which included the following (Acts 15:28-29):
For it seemed good to the Holy Ghost, and to us, to lay upon you no greater burden than these necessary things; That ye abstain from meats offered to idols, and from blood, and from things strangled, and from fornication: from which if ye keep yourselves, ye shall do well.
Circumcision was not required. Most of the laws of kashrut (kosher) were not required to be followed by Gentiles. No mention of the Ten Commandments is made. In particular for this discussion, Gentile Christians were not required to keep Sabbath or any other of the appointed holy days of the Jews. To hold that one must keep Sabbath in accordance with the Ten Commandments is in direct contradiction with the apostle Peter and other followers of Jesus in the first century.
I will contend that it would actually be good for most of us to keep Sabbath. In America in the twenty-first century we don't often take a day of rest. Our days off are filled with all the chores we couldn't do during our workweek. But to require it of my family or any other non-Jewish Christian would be to fly in the face of scripture.