Our passage reads: “And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads: 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. Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six.”
It is my conviction that God would not leave people in the dark concerning this most important end-time issue. Those who will gain victory over the beast—surviving its deceptions and assaults—would/must clearly understand the issues at stake. The prophecy of Daniel intimates us that God will grant special illumination to His faithful in the “time of the end.”: “Many shall be purified, and made white, and tried; but the wicked shall do wickedly: and none of the wicked shall understand; but the wise shall understand” (Dan. 12:9, 10, Emphasis mine). It is pertinent to note that understanding come to those who are the opposite of the wicked. They are wise because, first and foremost, they are righteous—they are true to the truth previously revealed to them (regarding stealing, adultery, state of the dead, Sabbath, etc.). So being righteous is a foremost prerequisite in receiving divine illumination.
Now the context in which our passage finds itself is undoubtedly dealing with the issue of worship. In fact, the entire book of Revelation is replete with this motif.
Another thing (very pivotal) that needs to be considered in knowing what the mark of the beast constitutes is to see the polarization shown in the book of Revelation. Most people follow the beast and a few follow the Lamb. Those who follow the Lamb do not receive the mark of the beast. They are characterized as those who keep the commandments of God in Revelation 14:12 and this is how they resisted the mark of the beast. From this alone it is safe to conclude that if one keeps all of God’s commandments by the enabling power of the Holy Spirit as a love commitment to Christ, one is bound to escape the mark of the beast.
Furthermore, taking the Bible as one corpus, it is also very easy to see what the issue will be in these last days. But before we even do that let us understand that once we are able to identify who the beast represents, we are not very far from knowing what its mark constitutes. And, of course, real, unbiased, textual, contextual, intertextual and objective studies have shown that the papal system of the medieval ages is the sea beast of Revelation 13. All the identifying marks unmistakably point to this religio-political power as the apocalyptic culprit that persecuted God’s people and tampered with His law in the Dark Ages (see our article “Who is the Beast with the Dreaded Mark?” on this blog).
Let us go back to looking at the entire corpus of Scripture in determining the mark of the beast. God has used different signs to mark His people down through the ages—entering the ark, circumcision, etc. But since we have been intimated in Revelation that those who do not receive the mark of the beast keep all of God’s commandments, it is only logical that God’s seal has everything to with God’s commandments.
It is important at this point to show that among the Ten Commandments there is only one that God speaks of as a sign between Him and His people (see Exo. 31:16, 17; Eze. 20:12, 20). It also makes sense to see that this is so because this is the only commandment that contains the reason why God alone is worthy of worship—by virtue of being the Creator God. It is not hard to see also that Satan would especially hate this commandment and seek to draw people’s attention from it—exactly what he has done through the ages. Have you ever noticed that even communist (atheistic) states had laws that prohibit stealing and murder? But such godless systems can never think of observing the Sabbath because the only reason for keeping it is to acknowledge the God who made the world in six literal, 24 hours, consecutive and contiguous days (Gen. 1:1-2:33; Exo. 20:8-11).
Moreover, the beast power has claimed that the greatest mark of its authority is the fact that it changed the Sabbath to Sunday and that those who keep Sunday are paying homage “to the authority the [Catholic] church.’’ And if we know that the mark of the beast is the opposite of God’s mark or seal (that Satan has created not only a spurious but also a counterfeit Sabbath), then it is not hard to figure out that faithful Sabbath observance in the last days constitute the seal of God and enforced Sunday observance and the prohibition of free Sabbath worship constitute the final issue around which the great controversy winds up on the earth. Remember, it’s not just a matter of days but that of those who you follow—the beast or the Lamb. And if Ellen White’s statement, as found in The Desire Of Ages, that “in order to keep the Sabbath holy, men themselves must be holy” is true, then true Sabbath observance calls for unreserved consecration to God. It is no wonder Ezekiel links Sabbath observance to sanctification (Eze. 20:12).
Finally, as a Seventh-day Adventist who believes that Ellen White manifested the gift of prophecy in her life and ministry, I fully subscribe to the following from The Great Controversy (which I believe to be prophetic):
But when Sunday observance shall be enforced by law, and the world shall be enlightened concerning the obligation of the true Sabbath, then whoever shall transgress the command of God, to obey a precept which has no higher authority than that of Rome, will thereby honor popery above God. He is paying homage to Rome, and to the power which enforces the institution ordained by Rome. He is worshiping the beast and his image. As men then reject the institution which God has declared to be the sign of His authority, and honor in its stead that which Rome has chosen as the token of her supremacy, they will thereby accept the sign of allegiance to Rome—“the mark of the beast.” And it is 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, that those who continue in transgression will receive “the mark of the beast.”
 Mgr. Segur, Plain Talk About the Protestantism of Today, p. 213 (Emphasis mine)
 Ellen G. White , The Desire of Ages (Seoul, Korea: Everlasting Gospel Publishing Association) p. 283
 Ellen G. White, The Great Controversy (Seoul, Korea: Everlasting Gospel Publishing Association), p. 449