Which day is the Sabbath? Since most churches observe Sunday as their day of rest and worship, many people assume that Sunday is the Sabbath.
The Fourth Commandment states: "Remember the Sabbath day, to keep it holy. Six days you shall labor and do all your work, but the seventh day is the Sabbath of the Lord your God. In it you shall do no work . . ." (Exodus 20:8-10 Exodus 20:8-10  Remember the sabbath day, to keep it holy.
 Six days shall you labor, and do all your work:
 But the seventh day is the sabbath of the LORD your God: in it you shall not do any work, you, nor your son, nor your daughter, your manservant, nor your maidservant, nor your cattle, nor your stranger that is within your gates:
American King James Version×, emphasis added throughout).
God commanded that the seventh day be observed as the Sabbath. A glance at almost any dictionary, encyclopedia or calendar will show you that Saturday is the seventh day of the week, while Sunday is the first day of the week. According to God's calendar, the seventh day is—and always has been—the Sabbath day. Although man has modified calendars through the centuries, the seven-day weekly cycle has remained intact throughout history. The days of the week have always remained in their proper order, with Sunday as the first day of the week and Saturday as the seventh.
Time has not been lost in this regard, as some assert. "The oracles of God"—His divine words and instructions—were entrusted to the Jewish people (Romans 3:1-2 Romans 3:1-2  What advantage then has the Jew? or what profit is there of circumcision?
 Much every way: chiefly, because that to them were committed the oracles of God.
American King James Version×), and they have preserved the knowledge of the seventh-day Sabbath faithfully since well before Christ's time to this day. Jesus repeatedly confirmed that the day the Jews observed as the Sabbath in His day was indeed the Sabbath. And since then the Jewish people, even scattered in many nations and in different sects, have all preserved the same day.
Moreover, the mainstream Christian churches, though rejecting the Sabbath, indirectly confirm when it is by maintaining their early tradition of worshipping on Sunday, which they acknowledge to be the first day of the week. Obviously that makes the previous day the seventh—the biblical Sabbath.
No biblical authorization for changing the Sabbath
So how did Sunday become the primary day of rest and worship for these churches? Although the concept of rest has largely disappeared today, most denominations continue to hold their worship services on Sunday. You can search throughout the Bible, but you will find no authority to alter the day of worship.
James Cardinal Gibbons, Catholic educator and archbishop of Baltimore at the turn of the 20th century, was blunt about the change:
"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. The Catholic Church correctly teaches that our Lord and His Apostles inculcated certain important duties of religion which are not recorded by the inspired writers . . . We must, therefore, conclude that the Scriptures alone cannot be a sufficient guide and rule of faith"(The Faith of Our Fathers, 1917, p. 89).
Did you grasp what he said? He admitted that Sunday observance is nowhere authorized in the Bible and that the seventh day is the only day sanctified by the Scriptures. His justification for changing the day of rest and worship assumes that authority exists apart from the Bible to define the necessary truths and practices for salvation—in other words, he says, human beings can change the commandments of God!
Change to Sunday was made after the New Testament was written
The change from Sabbath to Sunday is not found anywhere in the Bible. It was made long after the writing of the New Testament. So how and when was the change made?
Initially Christianity was viewed as simply a sect of Judaism. However, after Jewish revolts in Judea in A.D. 67-70 and 132-135, Jewish religious practices—many of which continued in the early Church—came to be viewed with hostility throughout the Roman Empire. Many among the Church began to abandon these practices, including observance of the biblical Sabbath and festivals.
No clear references to Sunday as a day of Christian worship are found until the writings of Barnabas and Justin, around A.D. 135 and 150, respectively. Observance of Sunday as the primary day of worship appears to have begun to solidify during the reign of Emperor Hadrian (A.D. 117-135), who harshly persecuted Jews throughout the Roman Empire. Hadrian specifically prohibited practices of Judaism, including observance of the seventh-day Sabbath.
These oppressive measures apparently influenced many early Christians in Rome to abandon the seventh day and turn to Sunday, the day for honoring the sun god among the Romans and other peoples of the ancient world. When Christianity was declared the official religion of the Roman Empire in the fourth century, the process accelerated.
Constantine's anti-Jewish prejudice
The Roman Emperor Constantine, although a worshipper of the sun, was the first emperor to profess belief in Christianity. But the "Christianity" Constantine endorsed was already considerably different from that practiced by Jesus and the apostles. The emperor accelerated the change by his own hatred of Jews and religious practices he considered Jewish.
For example, at the Council of Nicea (A.D. 325), church authorities essentially banned the biblical Passover observance. Endorsing this change, Constantine announced: "It appeared an unworthy thing that . . . we should follow the practice of the Jews, who have impiously defiled their hands with enormous sin, and are, therefore, deservedly afflicted with blindness of soul . . . Let us then have nothing in common with the detestable Jewish crowd" (Eusebius, Life of Constantine 3, chapter 18, quoted in Nicene and Post-Nicene Fathers, 1979, Vol. 1, pp. 524-525).
In a bid to unify his empire, he established the first laws making Sunday the official day of rest. His A.D. 321 law, for example, stated: "On the venerable Day of the Sun [Sunday] let the magistrates and people residing in cities rest, and let all workshops be closed."
Several decades later, the Council of Laodicea decreed: "Christians must not judaize by resting on the Sabbath, but must work on that day, rather honoring the Lord's Day [Sunday]; . . . But if any shall be found to be judaizers, let them be anathema from Christ."
Within a few centuries observance of the biblical Sabbath was driven underground within the confines of the empire, and most who professed Christianity embraced Sunday.
Although the Protestant Reformation brought some changes, observance of Sunday continued from the Roman Catholic Church into subsequent Protestant denominations. But whereas the Catholic Church claimed authority to establish its own times of worship, Protestant churches generally justified Sunday observance on the grounds that the seventh-day Sabbath was replaced in the New Testament by worship on Sunday in honor of Christ's resurrection.
However, as confirmed by Cardinal Gibbons above, there is no biblical authority for changing the day of rest and worship from the seventh day to Sunday. As shown throughout this booklet, Jesus Christ, the apostles, and Jewish and gentile members of the early Church alike continued to observe the seventh-day Sabbath—the only day authorized in the Bible.