The key to this one can be found in the very name… [Sun]day. From the beginning to the end of the Bible there is not a single passage that warrants the transfer of the Sabbath from the seventh day of the week to the first. True Christians have always maintained obedience to the fourth commandment and kept the seventh day Sabbath. History shows the official day change began with the Roman Emperor Constantine on March 7, 321 AD, when he passed an edict requiring Sunday, “the venerable day of the Sun”, to be kept as a day of rest in favour of Sun worship as was customary in ancient Babylon and with the pagans. This change was finalized by the Papacy of the Roman Catholic church in 363-364 AD, for which they still claim credit for.

The Sabbath was almost murdered out of existence throughout the terrible 1260 years (538-1798 AD) of the “dark ages”, when the Roman Catholic church ruled as church and state. Many Christians were tortured and killed by the Roman Catholic church for keeping the seventh day Sabbath. Even to this day the Roman Catholic church claims authority to be able to change both “the times” and “the law” (see Daniel 7:25) – this is clearly manifested in their changing of the Ten Commandments (the complete removal of 2nd commandment on idolatry, the changing of the 4th commandment to “The Lord’s Day” meaning [Sun]day, and to maintain 10, the splitting the 10th commandment in two, becoming the 9th and 10th).

Ultimately, the seventh day is the only day blessed and made holy by God as the Sabbath. “So then, there remains a Sabbath rest for the people of God, for whoever has entered God's rest has also rested from his works as God did from His. Let us therefore strive to enter that rest, so that no one may fall by the same sort of disobedience. For the word of God is living and active, sharper than any two-edged sword, piercing to the division of soul and of spirit, of joints and of marrow, and discerning the thoughts and intentions of the heart. And no creature is hidden from His sight, but all are naked and exposed to the eyes of Him to whom we must give account.” Hebrews 4:9-13.

"Of course the Catholic Church claims that the change (Saturday Sabbath to Sunday) was her act... And the act is a MARK of her ecclesiastical authority in religious things." H.F. Thomas, Chancellor of Cardinal Gibbons. Nov. 11, 1895

"Sunday is our MARK or authority. . .the church is above the Bible, and this transference of Sabbath observance is proof of that fact" Catholic Record of London, Ontario Sept 1,1923.

"Sunday is founded, not of scripture, but on tradition. As there is no scripture for the transfer of the day of rest from the last to the first day of the week, Protestants ought to keep their Sabbath on Saturday and thus leave Catholics in full possession of Sunday." - Catholic Record, September 17, 1893.

"Some have suffered torture because they would not rest when others kept Sunday, for they declared it to be the holiday and law of Antichrist." - Sebastian Frank, AD 1536. By this time in history the Seventh day Sabbath was severely under attack.

"Sunday...It is the law of the Catholic Church alone..." American Sentinel (Catholic) June 1893 "The Catholic church," declared Cardinal Gibbons, "by virtue of her divine mission changed the day from Saturday to Sunday." Catholic Mirror Sept. 23 1983. (Official organ of Cardinal Gibbons)

"The Bible says, Remember that thou keep holy the Sabbath day. The Catholic church says, No! By my divine power I abolish the Sabbath day, and command you to keep the first day of the week. And lo, the entire civilized world bows down in reverent obedience to the command of the holy Catholic church!" Father Enright, C.S.S.R. of the Redemptoral College, Kansas City, History of the Sabbath, p. 802

Many more quotes can be found here: https://remnantofgod.org/beastword.htm#SABBATH