If you are under the impression that the Catholics keep Sunday because of biblical grounds--you are mistaken. This is from the Catholics themselves--again--not from SDA's.
The Convert’s Catechism of Catholic Doctrine by: Peter Geiermann, C. SS. R. (published by: B. Herder Book Co. -1946)
3. The Third Commandment:
Q. What is the Third Commandment?
A. The Third Commandment is: Remember that thou keep holy the Sabbath day.
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 transferred the solemnity from Saturday to Sunday.
Q. Why did the Catholic Church substitute Sunday for Saturday?
A. The Church substituted Sunday for Saturday, because Christ rose from the dead on a Sunday, and the Holy Ghost descended upon the Apostles on a Sunday.
Q. By what authority did the Church substitute Sunday for Saturday?
A. The Church substituted Sunday for Saturday by the plenitude of that divine power which Jesus Christ bestowed upon her.
Q. What does the Third Commandment command?
A. The Third Commandment commands us to sanctify Sunday as the Lord’s Day.
Q. What does the Third Commandment forbid?
A. The Third Commandment forbids (1) The omission of prayer and divine worship; (2) All unnecessary servile work; (3) Whatever hinders the keeping of the Lord’s Day holy.
Q. Is the desecration of the Lord’s Day a grievous matter?
A. The desecration of the Lord’s Day is a grievous matter in itself, though it admits of light matter."
“It is well to remind the Presbyterians, Baptists, Methodists, and all other Christians, that the Bible does not support them anywhere in their observance of Sunday.
Sunday is an institution of the Roman Catholic Church, and those who observe the day observe a commandment of the Catholic Church
.” Priest Brady, in an address, reported in the Elizabeth, NJ ‘News’ on March 18, 1903.
"Protestants ... accept Sunday rather than Saturday as the day for public worship after the Catholic Church made the change... But the Protestant mind does not seem to realize that ... in observing Sunday, they are accepting the authority of the spokesman for the Church, the pope."
Our Sunday Visitor
, February 5th, 1950.
. Have you any other way of proving that the Church has power to institute festivals of precept?
A. Had she not such power, she could not have done that in which all modern religionists agree with her; —she could not have substituted the observance of Sunday the first day of the week, for the observance of Saturday the seventh day, a change for which there is no Scriptural authority. Rev. Stephen Keenan, A Doctrinal Catechism; New York in 1857, page 174
"All of us believe many things in regard to religion that we do not find in the Bible. For example, 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 Church outside the Bible." The Catholic Virginian, "To Tell You The Truth,” Vol. 22, No. 49 (Oct. 3, 1947).
"... 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 Faith of Our Fathers, by James Cardinal Gibbons, Archbishop of Baltimore, 88th edition, page 89. Originally published in 1876, republished and Copyright 1980 by TAN Books and Publishers, Inc., pages 72-73.