If you fear the Lord and serve Him and obey His voice, and do not rebel against the commandment of the Lord, then both you and the king who reigns over you will continue following the Lord your God. However, if you do not obey the voice of the Lord, but rebel against the commandment of the Lord, then the hand of the Lord will be against you, as it was against your fathers.--1 Samuel 12:14-15
The sign or seal of God is the observance of the seventh day Sabbath, the Lord's memorial of His work of creation. "The Lord spake unto Moses saying, Speak thou also unto the children of Israel, saying, 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." Here the Sabbath is clearly defined as a sign between God and His people.
The mark of the beast is the opposite of this, the observance of the first day of the week. This mark distinguishes those who acknowledge the supremacy of the Papal authority, seen in the man of sin thinking to change times and laws, and those who acknowledge the authority of God.
A refusal to obey the commandments of God, and a determination to cherish hatred against those who proclaim these commandments leads to the most determined war on the part of the dragon, whose whole energies are brought to bear against the commandment-keeping people of God. "He causeth all both small and great, to receive a mark in their right hand, or in their foreheads." Not only are men not to work with their hands on Sunday, but with their minds they are to acknowledge Sunday as the Sabbath. "And that no man might but or sell, save he that had the mark of the number of his name." (Manuscript 1, January 11, 1897)
REFLECTION: On which side are we ranging ourselves? On the side of the dragon, who was wroth with the woman, and went to make war with the remnant of her seed, who keep the commandments of God and have the testimony of Jesus Christ?