The Sealing is the placing of the Seal of God, by the Holy Spirit, in one’s forehead, or mind. This seal is given as a guard against deception by satan and a protection from receiving the mark of the beast. Once a person is sealed, they cannot be led astray from God and cannot be deceived into worshipping antichrist and his system (Matthew 24, Mark 13, Luke 21). This sealing is a part of the Gospel Armor, the belt of truth, and all sealing will be complete before the arrival of antichrist (Revelation 7).
In the end times, this seal is not only given to ensure someone does not receive the mark of the beast, but also it protects them from being tormented by the fallen angels who will be returning to earth with satan during the tribulation (Rev 7:1-3, 9:1-5).
When God seals one of His elect with the Holy Spirit, He reveals His mysteries to that servant of God so that the person’s understanding of His Word can be complete (Matthew 4:10-12, 13:10-17, Luke 8:9-10, Romans 16:25-27, 1 Corinthians 4:1, 13:2, Ephesians 1:3-9, 3:1-6, 6:18-20, Colossians 1:23-29). Once someone has this understanding, and his spiritual eyes are opened, it is his responsibility to share this light of truth with others and not hide it from view. He must plant seeds of truth so that it may benefit others and allow them to be sealed if they are meant to have this truth as well.
With this sealing, and refusing to bow to antichrist, comes also a risk of being delivered up to testify as to why you refuse (Matthew 10:17-24, Mark 13:9-13, Luke 21:12-15, Revelation 2:10), and God knows that not everyone can handle this pressure because of how they performed in the first earth age (Romans 8:28-34, 11:1-14). For this reason, most people of the world are blinded from this deeper understanding of His truth, and God will not allow them to understand no matter how intelligent they may be. This is meant as a protection for them, because if they were allowed to see these truths and were delivered up to testify, they would buckle under the pressure and would cave in and bow to antichrist knowing full well that he is not Jesus, the true Messiah. This would be a grave sin. Because God loves them, and because they are not dedicated enough to studying the Bible, and standing against satan, and his power and deception, He allows them to be deceived (Romans 11:7-14, 2 Thessalonians 2:7-12) so they may learn a lesson they can take with them into the Millennium, with hopes they will make the right decisions at that time.
This sealing is an awesome blessing and an awesome responsibility at the same time.