The change is connected in part to waves of anti-Semitism that swept the Roman Empire as a result of the Jewish wars in the first and second centuries. At that time, many among the scattered early Christians erroneously began to distance themselves from biblical practices that were commonly viewed as Jewish. This included obeying God's Sabbath command.
Simultaneously, false teachers arose from within the Church just as the apostle Paul had prophesied (Acts 20:29-30), introducing pagan teachings and beliefs. Over time, the majority of those professing to be Christians drifted from the original teachings and practices of Christ and the apostles. (This history is spelled out in more detail in our free booklet The Church Jesus Built.)
In the third and fourth centuries, as the Catholic Church gained favor in the Roman Empire under the emperor Constantine the Great, it increasingly incorporated customs adapted from pagan worship (a process called syncretism). Among these was the elevation of Sunday, the day devoted to honoring the sun god, a deity worshipped by Constantine and very popular with the masses in the Roman Empire.
Meanwhile, those who held to the original teachings of Christ and the apostles were increasingly persecuted. By A.D. 365 an edict by Catholic leaders at the Council of Laodicea declared: "Christians must not Judaize by resting on the Sabbath, but must work on that day, rather, honouring the Lord's Day [meaning Sunday in this context]; and, if they can, resting then as Christians. But if any shall be found to be Judaizers, let them be anathema from Christ [i.e., excommunicated or disfellowshipped]" (Nicene and Post-Nicene Fathers, vol. 19, p. 148, emphasis added).
Most Catholic and some Protestant theologians are willing to admit that Sunday observance cannot be justified from the Scriptures. Notice what James Cardinal Gibbons, archbishop of Baltimore early in the last century, wrote in The Faith of Our Fathers: "Is not every Christian obliged to sanctify Sunday and to abstain on that day from unnecessary servile work? Is not the observance of this law among the most prominent of our sacred duties? But you may read the Bible from Genesis to Revelation, and you will not find a single line authorizing the sanctification of Sunday. The Scriptures enforce the religious observance of Saturday, a day which we never sanctify" (1917, p. 89, emphasis added).
The truth about other important aspects of the Saturday/Sunday controversy is addressed in our free booklet Sunset to Sunset: God's Sabbath Rest. GN