In Revelation 7 an angel places the “seal of the living God” on the servants of God “in their foreheads” (Revelation 7:3). The Bible explains exactly what this means.
Ephesians 1:13 states that people are “sealed with [the] holy Spirit of promise.” Another Bible verse reveals that the Holy Spirit does this sealing work by writing in people’s hearts: “Forasmuch as ye are manifestly declared to be the epistle of Christ ministered by us, written not with ink, but with the Spirit of the living God; not in tables of stone, but in fleshy tables of the heart” (2 Corinthians 3:3).
What, then, does the Holy Spirit write in people’s hearts in order to “seal” them with the seal of God? Hebrews 10:15-16 gives the answer: “Whereof the Holy Ghost also is a witness to us, for after that he had said before, This is the covenant that I will make them them after those days, saith the Lord, I will put my laws into their hearts, and in their minds will I write them.” Revelation’s seal of God is received as people allow the Holy Spirit to write the law of God in their minds and hearts. And the sign of that sealing process is the seventh-day Sabbath. “It [the Sabbath] is a sign between me and the children of Israel for ever: for in six days the Lord made heaven and earth, and on the seventh day he rested” (Exodus 31:17).