The Seal of God and the Mark of the Beast
Last Day Events
Page 222

In the Sealing Time Now:  I saw that the present test on the Sabbath could not come until the mediation of Jesus in the holy place was finished and He had passed within the second veil; therefore Christians who fell asleep before the door was opened into the most holy, when the midnight cry was finished, at the seventh month, 1844, and who had not kept the true Sabbath, now rest in hope, for they had not the light and the test on the Sabbath which we now have since that door was opened. I saw that Satan was tempting some of God's people on this point. Because so many good Christians have fallen asleep in the triumphs of faith and have not kept the true Sabbath, they were doubting about its being a test for us now. . .

God's Test of Loyalty
In Heavenly Places
Page 150

God has a test for us, and if we come up to the standard we shall be a peculiar people. The Sabbath draws a separating line between us and the world, not faintly but in plain, distinct colors. To those who have received the light of this truth the Sabbath is a test; it is not a human requirement, but God's test. It is what will distinguish between those who serve God and those who serve Him not, and upon this point will come the last great conflict between truth and error. All who profess to keep God's law should stand united in the sacred observance of His holy Sabbath. . . .

The Third Angel's Message
The Spirit of Prophecy Volume Four
Page 281

That institution which points to God as the Creator is a sign of his rightful authority over the beings he has made. The change of the Sabbath is the sign, or mark, of the authority of the Romish Church. Those who, understanding the claims of the fourth commandment, choose to observe the false in place of the true Sabbath, are thereby paying homage to that power by which alone it is commanded. The change in the fourth commandment is the change pointed out in the prophecy, and the keeping of the counterfeit Sabbath is the reception of the mark. But Christians of past generations observed the first day, supposing that they were keeping the Bible Sabbath, and there are in the churches of to-day many who honestly believe that Sunday is the Sabbath of divine appointment. None of these have received the mark of the beast. There are true Christians in every church, not excepting the Roman Catholic communion. The test upon this question does not come until Sunday observance is enforced by law, and the world is enlightened concerning the obligation of the true Sabbath. Not until the issue is thus plainly set before the people, and they are brought to choose between the commandments of God and the commandments of men, will those who continue in transgression receive the mark of the beast.

God's Special Sign
Our High Calling
Page 343

As the tree of knowledge was placed in the midst of the Garden of Eden, so the Sabbath command is placed in the midst of the Decalogue. In regard to the fruit of the tree of knowledge, the restriction was made, "Ye shall not eat of it, . . . lest ye die." Gen. 3:3. Of the Sabbath God said, Ye shall not defile it, but keep it holy. "Remember the sabbath day, to keep it holy." Ex. 20:8. As the tree of knowledge was the test of Adam's obedience, so the fourth command is the test that God has given to prove the loyalty of all His people.

The Last Great Struggle
Selected Messages Book 3
Page 423

The Sabbath Is the Issue in the Final Conflict:  The Sabbath is the great test question. It is the line of demarkation between the loyal and true and the disloyal and transgressor. This Sabbath God has enjoined, and those who claim to be commandment keepers, who believe that they are now under the proclamation of the third angel's message, will see the important part the Sabbath of the fourth commandment holds in that message. It is the seal of the living God. They will not lessen the claims of the Sabbath to suit their business of convenience.--Manuscript 34, 1897.

The Final Warning
The Great Controversy [1888 edition]
Page 605

The Sabbath will be the great test of loyalty; for it is the point of truth especially controverted. When the final test shall be brought to bear upon men, then the line of distinction will be drawn between those who serve God and those who serve him not. While the observance of the false sabbath in compliance with the law of the State, contrary to the fourth commandment, will be an avowal of allegiance to a power that is in opposition to God, the keeping of the true Sabbath, in obedience to God's law, is an evidence of loyalty to the Creator. While one class, by accepting the sign of submission to earthly powers, receive the mark of the beast, the other, choosing the token of allegiance to divine authority, receive the seal of God

Remember the Sabbath Day to keep it Holy
Lake Union Herald

Remember the Sabbath Day to Keep it Holy. By Mrs. E. G. White.

Letters have come to me from several persons with the request that I should write in regard to the manner in which we should observe the Sabbath. We have the Bible plain and clear upon this subject. We should not leave the work of the six working days to be done on the Sabbath. Through Moses the Lord said to the children of Israel, "To-morrow is the rest day of the holy Sabbath of the Lord; bake that which you will bake to-day, and seethe that which ye will seethe, and that which is left lay up to keep until the morning." "The manna was like coriander seed, and the color like bdellium. And the people went about and gathered it, and ground it in the mills or beat with a mortar and baked it in pans and made cakes of it." Thus there was something to be done in the preparing even of the heaven-sent bread for the children of Israel. This was a test for them. God desired to see whether or not they would keep the Sabbath holy. The Lord told the children of Israel that this work must be done on the preparation day--Friday. On that day they were to bake that which they would bake and seethe that which they would seethe.

Words of Warning
The Signs of the Times

The Sabbath, sanctified and blessed by God, was designed as His great memorial of creation. It is ever to stand unmoved, a rock of offense, as Christ was to the Jewish nation. The Sabbath is the test to-day, as Christ was a test to the Jews.

God's Claims are First
God's Amazing Grace
Page 59

The Sabbath is the Lord's test, and no man, be he king, priest, or ruler, is authorized to come between God and man. Those who seek to be conscience for their fellow men, place themselves above God. Those who are under the influence of a false religion, who observe a spurious rest day, will set aside the most positive evidence in regard to the true Sabbath. They will try to compel men to obey the laws of their own creation, laws that are directly opposed to the law of God. . . . The law for the observance of the first day of the week is the production of an apostate Christendom. . . . In no case are God's people to pay it homage.

Satan Personates Christ
Page 205

He will declare that the Sabbath has been changed from the seventh to the first day of the week; and as lord of the first day of the week he will present this spurious sabbath as a test of loyalty to him.

Revelation 14
S.D.A. Bible Commentary Vol. 7
Page 976

This is the test that the people of God must have before they are sealed. All who proved their loyalty to God by observing His law, and refusing to accept a spurious sabbath, will rank under the banner of the Lord God Jehovah, and will receive the seal of the living God. Those who yield the truth of heavenly origin and accept the Sunday sabbath, will receive the mark of the beast (Letter 11, 1890).

Israel and the Law
The Signs of the Times

The Sabbath was placed in the decalogue as the seal of the living God, pointing out the Law-giver, and making known his right to rule. It was a sign between God and his people, a test of their loyalty to him. Moses was commanded to say to them from the Lord: "Verily my Sabbaths ye shall keep; for it is a sign between me and you throughout your generations; that ye may know that I am the Lord that doth sanctify you." And when some of the people went out on the Sabbath to gather manna, the Lord asked, "How long refuse ye to keep my commandments and my laws?" -

Source: EGW Website