There is no record in the New Testament stating that churches in the first century ever kept Sunday as a day of religious worship. The origin of Sunday worship, according to historians, was post-apostolic:

The first Christian church established at Jerusalem by apostolic authority became its doctrine and practice a model for the greater part of those founded in the first century…These Judaizing Christians were first known by the outside world as ‘Nazarenes’…All Christians agreed in celebrating the seventh day of the week in conformity to the Jewish converts. (Schaff, Phillip, The History of the Christian Church, [Grand Rapids, Michigan: WM. B. Eerdman’s, 1994], 7:50, 51, 69)

The Sabbath had been a prominent feature in the Jewish creed and practice, and since much bitter prejudice grew up between the pagan converts and the Jewish elements in the church, the heathen element gradually gained control, and succeeded in effacing much of what they considered Judaistic. The fact that Justin Martyr and others began to press their antinomian theories shows that the Sabbath was yet an institution which had a strong hold on the church, even on the Gentile converts. The Sabbath was not discarded during the apostolic days. (John Kiesz, “A History of the Sabbath and Sunday” in Christian Resource Centre (Bermuda) Version 2001.1 [January 26, 2001])

The apostle Paul had warned the early Christians concerning the falling away of the church:

For I know this, that after my departure savage wolves will come in among you, not sparing the flock. Also from among yourselves men will rise up, speaking perverse things, to draw away the disciples after themselves. (Acts 20:29-30)

For fifty years after St. Paul’s life, a curtain hangs over the church, through which we vainly strive to look; and when at last the curtain rises, about A.D. 120, with the writings of the earliest church fathers, we find a church in many aspects very different from that in the days of St. Peter and St. Paul. (Jesse L. Hurlbut, The Story of the Christian Church [Grand Rapids, Michigan: Zondervan, 1986], 41)

God had revealed through the prophecy of Daniel that during the “fourth kingdom,” the Roman Empire, the saints of the Most High would be persecuted. The “fourth beast,” the Roman Emperor, “shall intend to change times and law” (Dan 7:23-25). His prophecy is amazingly accurate.

Constantine was emperor of Rome from A.D. 306 to 337. He was a worshiper of the sun during the first years of his reign, but later professed conversion to Christianity. The Emperor Constantine changed the observance of the seventh-day Sabbath to Sunday by law in A.D. 321:

On the venerable day of the sun let the magistrates and people residing in the cities rest, and let all workshops be closed. In the country, however, persons engaged in agriculture may freely and lawfully continue their pursuits; because it often happens that another day is not so suitable for grain growing or for vine planting; lest by neglecting the proper moment for such operations, the bounty of heaven should be lost.” – Given the 7th day of March, Crispus and Constantine being consuls each of them for the second time. (Codex Justinianus 3.12-3, translated by Philip Schaff, in History of the Christian Church [Grand Rapids, Michigan: WM. B. Eerdman’s, 1994] 3:380)

Unquestionably the first law, either ecclesiastical or civil, by which the Sabbatical observance of that day is known to have been ordained, is the edict of Constantine, 321 A.D. (Chambers’ Encyclopedia, n.d., s.v. “Sabbath”)

The Roman Catholic Church neither denies nor attempts to conceal this substitution of Sunday for the Sabbath. The Catholic Church bases Sunday observance on the authority of the Pope and not on the Holy Bible. It regards the change as evidence of the Catholic Church’s power to change a commandment of God:

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. (James Cardinal Gibbons, The Faith of our Fathers, 1893 ed. [Baltimore, Maryland: Tan Books, 1917], 72-73)

The Convert’s Catechism of Catholic Doctrine, received the “Apostolic Bless” of Pope Pius X on January 25, 1910:

Question: Which is the Sabbath day? Answer: Saturday is the Sabbath day. Question: Why do we observe Sunday instead of Saturday? Answer: We observe Sunday instead of Saturday because the Catholic Church, in the Council of Laodecia (AD 336), transferred the solemnity from Saturday to Sunday. (2nd ed. St. Louis, Missouri: B. Herder Book Company: 1923], 50)

As a result of the Catholic Church’s change, however, Protestant, Evangelical, and other Christians, are greatly confused on the Sabbath issue.