Leaders and authorities from many religious denominations candidly acknowledge that Saturday is the biblical Sabbath day and that there is no biblical basis for Sunday observance. Notice below some of their admissions that the change was made by the Roman Catholic Church and not on the basis of biblical instruction.
Roman Catholic admissions
"Nowhere in the Bible do we find that Christ or the Apostles ordered that the Sabbath be changed from Saturday to Sunday. We have the commandment of God given to Moses to keep holy the Sabbath day, that is the 7th day of the week, Saturday. Today most Christians keep Sunday because it has been revealed to us by the [Roman Catholic] church outside the Bible" ("To Tell You the Truth," The Catholic Virginian, Oct. 3, 1947, p. 9).
"But since Saturday, not Sunday, is specified in the Bible, isn't it curious that non-Catholics who profess to take their religion directly from the Bible, and not the Church, observe Sunday instead of Saturday? Yes of course, it is inconsistent; but this change was made about 15 centuries before Protestantism was born, and by that time the custom was universally observed. They have continued the custom, even though it rests upon the authority of the Catholic Church and not upon an explicit text in the Bible" (Dr. John O'Brien, Faith of Millions, pp. 543-544).
"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, Faith of our Fathers, 88th ed., p. 89).
"Q: Which is the Sabbath day?
"A: Saturday is the Sabbath day.
"Q: Why do we observe Sunday instead of Saturday?
"A: We observe Sunday instead of Saturday because the Catholic Church, in the Council of Laodicea, transferred the solemnity from Saturday to Sunday" (Peter Geiermann, The Convert's Catechism of Catholic Doctrine, 1957, p. 50).
Protestants follow Rome's lead
"The Sabbath was binding in Eden, and it has been in force ever since. This fourth commandment begins with the word 'remember,' showing that the Sabbath already existed when God wrote the law on the tables of stone at Sinai. How can men claim that this one commandment has been done away with when they will admit that the other nine are still binding?" (Dwight L. Moody, Weighed and Wanting, pp. 47-48).
Anglican/Episcopal: "Where are we told in the Scriptures that we are to keep the first day at all? We are commanded to keep the seventh; but we are nowhere commanded to keep the first day . . . The reason why we keep the first day of the week holy instead of the seventh is for the same reason that we observe many other things, not because the Bible, but because the church has enjoined it" (Isaac Williams, Plain Sermons on the Catechism, 1882, Vol. 1, pp. 334, 336).
Baptist: "There was and is a commandment to keep holy the Sabbath day, but that Sabbath day was not Sunday. It will however be readily said, and with some show of triumph, that the Sabbath was transferred from the Seventh to the First day of the week . . . Where can the record of such a transaction be found? Not in the New Testament—absolutely not. There is no scriptural evidence of the change of the Sabbath institution from the Seventh to the First day of the week . . .
"To me it seems unaccountable that Jesus, during three years' discussion with His disciples, often conversing with them upon the Sabbath question . . . never alluded to any transference of the day; also, that during forty days of His resurrection life, no such thing was intimated . . .
"Of course I quite well know that Sunday did come into use in early Christian history . . . But what a pity that it comes branded with the mark of Paganism, and christened with the name of the sun-god, adopted and sanctioned by the Papal apostasy, and bequeathed as a sacred legacy to Protestantism" (Dr. Edward Hiscox, before a New York ministers' conference, Nov. 13, 1893, as reported in the New York Examiner, Nov. 16, 1893).
"There was never any formal or authoritative change from the Jewish seventh-day Sabbath to the Christian first-day observance" (William Owen Carver, The Lord's Day in Our Day, 1940, p. 49).
Congregationalist: "It is quite clear that however rigidly or devotedly we may spend Sunday, we are not keeping the Sabbath . . . The Sabbath was founded on a specific Divine command. We can plead no such command for the obligation to observe Sunday" (Dr. R.W. Dale, The Ten Commandments, 1884, p. 100).
Disciples of Christ: "The first day of the week is commonly called the Sabbath. This is a mistake. The Sabbath of the Bible was the day just preceding the first day of the week. The first day of the week is never called the Sabbath anywhere in the entire Scriptures. It is also an error to talk about the change of the Sabbath from Saturday to Sunday. There is not in any place in the Bible any intimation of such a change" (Alexander Campbell, First Day Observance, pp. 17, 19).
Lutheran: "But they err in teaching that Sunday has taken the place of the Old Testament Sabbath and therefore must be kept as the seventh day had to be kept by the children of Israel . . . These churches err in their teaching, for Scripture has in no way ordained the first day of the week in place of the Sabbath. There is simply no law in the New Testament to that effect" (John Theodore Mueller, Sabbath or Sunday, pp. 15-16).
Methodist: "Take the matter of Sunday. There are indications in the New Testament as to how the church came to keep the first day of the week as its day of worship, but there is no passage telling Christians to keep that day or to transfer the Jewish Sabbath to that day" (Harris Franklin Rall, Christian Advocate, July 2, 1942, p. 26).
Presbyterian: "The Sabbath is a part of the Decalogue—the Ten Commandments. This alone forever settles the question as to the perpetuity of the institution . . . Until, therefore, it can be shown that the whole moral law has been repealed, the Sabbath will stand . . . The teaching of Christ confirms the perpetuity of the Sabbath" (T.C. Blake, D.D., Theology Condensed, pp. 474-475).
Does it matter to God?
Jesus Christ condemned the practices of the religious leaders of His day, saying: "'In vain they worship Me, teaching as doctrines the commandments of men.' For laying aside the commandment of God, you hold the tradition of men . . . All too well you reject the commandment of God, that you may keep your tradition" (Mark 7:7-9 Mark 7:7-9  However, in vain do they worship me, teaching for doctrines the commandments of men.
 For laying aside the commandment of God, you hold the tradition of men, as the washing of pots and cups: and many other such like things you do.
 And he said to them, Full well you reject the commandment of God, that you may keep your own tradition.
American King James Version×).
According to Christ's own statements, it is possible to worship Him in a way that does no good—that is, it is in vain. God does not give us the choice of how to worship Him—only whether we will worship Him according to His instructions or not. What, then, must He think of those who ignore His commands regarding the Sabbath, substituting instead a different day?