Duran, I agree with PetrW. Question is: When is the sealing to take place? Here's a few interesting facts about the sealing process. Jesus as God’s firstborn, would have been personally sealed by his Father during his ministry on earth (John 6:27; Col. 1:15). Afterwards his intimate disciples, including Paul, would have been sealed (2 Cor. 1:21, 22; Eph. 1:13; 4:30).
As to the actual sealing of the 144,000, I believe it is still future. The transition between chapters 6&7 of Revelation is introduced by the Greek phrase Καὶ μετὰτοῦτο (Rev. 7:1 Tischendorf’s New Testament, 8th edition; cf. NA28 footnote), “and after this,” “this” referring to the breaking of the sixth seal, specifically the kings of the earth and their followers, finding refuge in their underground shelters. This must still take place. It would be presumpteous to claim that you are one of the 144,000, like those in the Society do.
What helped me to establish a foundation to build my faith is a study of the prophecies. Peter said: "Pay attention as to a lamp shining in a dark place, until the day dawns and the morning star rises in your hearts, knowing this first of all, that no prophecy of Scripture comes from someone's own interpretation. For no prophecy was ever produced by the will of man, but men spoke from God as they were carried along by the Holy Spirit." (2 Pet. 1:19-21 ESV)
All are interested in the future. The angel told Daniel one of the reasons of prophecy is "to make you understand what is to happen to your people in the latter days. For the vision is for days yet to come." (Dan. 10:14 ESV). John in Revelation was invited to view future visions: "After this I looked, and behold, a door standing open in heaven! And the first voice, which I had heard speaking to me like a trumpet, said, "Come up here, and I will show you what must take place after this." (Rev. 4:1 ESV)