Seventh Day Adventistism teaches that the Catholic church is the antichrist and that Sunday is the mark of the beast spoken about in the Revelation of Jesus, ie. 13:17:
And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name.
The prophesies of Ellen White include predictions of a law that will once again require men to worship on Sunday. Here is one of her more famous statements:
I saw that the Sabbath commandment was not nailed to the cross. If it was, the other nine commandments were; and we are at liberty to break them all, as well as to break the fourth. I saw that God had not changed the Sabbath, for He never changes. But the pope had changed it from the seventh to the first day of the week; for he was to change times and laws [Daniel 7:25].<p style="text-align: right;"> Ellen White, _A word to the Little Flock, _page 18, paragraph 3, and _Early Writings,_ page 32, paragraph 3.
I do have a couple books from the Christians of a few centuries ago who regarded the Catholic church as Antichrist. I even agree with them to a certain extent. There are true Christians within the Catholic church but anybody who would withold the words of God from the individual has placed themselves in a very bad position. There are some possible fringe exceptions but as a general rule you do not want to be the one separating the people from God’s words.
Back to Sunday worship. According to Adventist apologetics, Pope Sylvester I (between 314 and 335 AD) overrode God’s decree that the 7th day of the week (Saturday) be the day of rest:
The Sabbath [Sylvester] commanded they call by the ancient name of the law, and the first [day] the Lords day, because the Lord rose on that day. Moreover the same pope ordered that the rest (otium) of the Sabbath would better be transferred to the Lords day, so that we should leave that day free of worldly works in order to praise God.<p style="text-align: right;"><span class="title"><font size="2">Rabanus Maurus, _De Clericorum Institutione_ (On the Institution of the Clergy), bk. 2, chap. 46, in _MPL_, Vol. 107, col. 361. Trans. from the Latin by Frank H. Yost.</font></span>
There is a lot more rhetoric at the link above, if you are interested. They make a big deal out of this decree by Pope Sylvester but then they cover their back by allowing that he simply made official what the church had already begun to do:
It should also be noted that Pope Sylvester did not invent Sunday worship, and neither did Emperor Constantine, and Adventists do not make that claim. But, it is evident to everyone that a change did happen to keeping Sunday instead of the Saturday Sabbath. Adventists have been well aware that celebrating the resurrection on Sundays predates the 4th century, though there is no biblical proof that the Apostles ever sanctioned a change of the Sabbath to Sunday or practiced it themselves.
No Biblical proof? Hmm. One Bible commentator by the name of Jamieson Fausset Brown points out John 20. In it you have the resurrection of Jesus and his talk with Mary Magdalene. That evening (explicitly the same day), Jesus appeared to the disciples as a group. This is the infamous moment when Thomas was absent. Verse 26 says:
And after eight days again his disciples were within, and Thomas with them: then came Jesus, the doors being shut, and stood in the midst, and said, Peace be unto you.
This eighth day is reckoned the same way that Jesus’ resurrection was reckoned to be after three days. It was a common counting practice among the Jews and meant that Jesus came to visit them again on the first day of the week. Even if you discount this explanation and were to believe that Jesus appeared to the disciples on the following Monday, verse 19 holds special interest:
Then the same day at evening, being the first day of the week, when the doors were shut where the disciples were assembled for fear of the Jews, came Jesus and stood in the midst, and saith unto them, Peace be unto you.
The Greek word for “week” is derived from the Hebrew language and literally means “Sabbath.” In the context it takes on the meaning “the first day of the week,” or perhaps “the first day from the sabbath.” Even the Adventist “Spirit of Prophesy Bible” (Luke 24:1, John is incomplete) translators agree that this word denotes the first day of the week in this context. It is universally accepted.
The reason I make this point is that the phrase appears again in Acts 20:7:
And upon the first day of the week, when the disciples came together to break bread, Paul preached unto them, ready to depart on the morrow; and continued his speech until midnight.
Paul also encouraged Christians to set aside money together on the first day of the week in I Corinthians 16:2:
Upon the first day of the week let every one of you lay by him in store, as God hath prospered him, that there be no gatherings when I come.
It was certainly not uncommon to meet on Sunday. By the end of John’s life (Revelation 1:10, circa 96 AD), it had become common to call the first day of the week “the Lord’s day.”
Justinus (~114-165 AD; also known as Justin Martyr) began his life as a disciple of Socrates and Plato. As a philosopher, he had dedicated himself to truth and this pressed him to argue the case of the persecuted Christians to the Roman rulers. The first Apology, or explanation, to the Roman emperor Antoninus Pius contains these words (all of chapter LXVII, emphasis mine):
<font face="none" size="-1">And we afterwards continually remind each other of these things. And the wealthy among us help the needy; and we always keep together; and for all things wherewith we are supplied, we bless the Maker of all through His Son Jesus Christ, and through the Holy Ghost. **And on the day called Sunday**, all who live in cities or in the country gather together to one place, and the memoirs of the apostles or the writings of the prophets are read, as long as time permits; then, when the reader has ceased, the president verbally instructs, and exhorts to the imitation of these good things. Then we all rise together and pray, and, as we before said, when our prayer is ended, bread and wine and water are brought, and the president in like manner offers prayers and thanksgivings, according to his ability, and the people assent, saying Amen; and there is a distribution to each, and a participation of that over which thanks have been given, and to those who are absent a portion is sent by the deacons. And they who are well to do, and willing, give what each thinks fit; and what is collected is deposited with the president, who succours the orphans and widows and those who, through sickness or any other cause, are in want, and those who are in bonds and the strangers sojourning among us, and in a word takes care of all who are in need. **But Sunday is the day on which we all hold our common assembly**, because it is the first day on which God, having wrought a change in the darkness and matter, made the world; and Jesus Christ our Saviour on the same day rose from the dead. For He was crucified on the day before that of Saturn (Saturday); and on the day after that of Saturn, which is the day of the Sun, having appeared to His apostles and disciples, He taught them these things, which we have submitted to you also for your consideration. </font>
There is not much with which to date this letter, but it was certainly written at least a century and a half before Sylvester became a pope. Sunday was already in widespread use by the Christian church. Clement of Alexandria (~150-215) even made mention of “Sunday School.”
Justinus lived in Rome. Clement lived in Egypt. This sort of discussion may well be what Paul meant when he wrote Romans 14:5,6:
One man esteemeth one day above another: another esteemeth every day alike. Let every man be fully persuaded in his own mind. He that regardeth the day, regardeth it unto the Lord; and he that regardeth not the day, to the Lord he doth not regard it. [...]
Whatever the case, I do not see any evidence that Sunday is such a mark of Satan’s work.