saying: ‘Do not harm the earth or the sea or the trees, until after we have sealed the slaves of our God in their foreheads.’”​—Revelation 7:2, 3.

 8. What is the sealing, and when did it begin?

⁸ What is this sealing, and who are these slaves of God? The sealing began at Pentecost 33 C.E. when the first Jewish Christians were anointed with holy spirit. Later, God proceeded to call out and anoint “people of the nations.” (Romans 3:29; Acts 2:1-4, 14, 32, 33; 15:14) The apostle Paul wrote about anointed Christians’ having a guarantee that they “belong to Christ” and added that God “has also put his seal upon us and has given us the token of what is to come, that is, the spirit, in our hearts.” (2 Corinthians 1:21, 22; compare Revelation 14:1.) Thus, when these slaves are adopted as God’s spiritual sons, they receive a token in advance of their heavenly inheritance​—a seal, or pledge. (2 Corinthians 5:1, 5; Ephesians 1:10, 11) They can then say: “The spirit itself bears witness with our spirit that we are God’s children. If, then, we are children, we are also heirs: heirs indeed of God, but joint heirs with Christ, provided we suffer together that we may also be glorified together.”​—Romans 8:15-17.

 9. (a) What endurance on the part of the remaining spirit-begotten sons of God is required? (b) For how long will the testing of the anointed go on?

⁹ “Provided we suffer together”​—what does that mean? In order to receive the crown of life, anointed Christians must endure, faithful even to death. (Revelation 2:10) It is not a matter of ‘once saved, always saved.’ (Matthew 10:22; Luke 13:24) Rather, they are admonished: “Do your utmost to make the calling and choosing of you sure for yourselves.” Like the apostle Paul, ultimately they must be able to say: “I have fought the fine fight, I have run the course to the finish, I have observed the faith.” (2 Peter 1:10, 11; 2 Timothy 4:7, 8) So here on earth the testing and sifting of the remaining spirit-begotten sons of God must go on until Jesus and his accompanying angels will have firmly implanted the seal ‘in the forehead’ of all of these, identifying them conclusively, irrevocably, as tried and faithful “slaves of our God.” That seal then becomes a permanent mark. Evidently, when the four winds of tribulation are unleashed, all of spiritual Israel will have been sealed in finality, even though a few will still be alive in the flesh. (Matthew 24:13; Revelation 19:7) The entire membership will be complete!​—Romans 11:25, 26.