How are the 144,000 sealed?
They are sealed with the mark of God in their foreheads. Coming out of the two witnesses' ministry in Jerusalem, the 144,000 receive this seal and then become evangelists and missionaries to the whole world during the final seven-year period.
Les explains that after the two witnesses come to Jerusalem and proclaim the Word of God again to Israel, the 144,000 come out of them. They are sealed with the mark of God in their foreheads, and then they become the evangelists and missionaries to the whole world. This sealing is part of the final seven-year period, which begins with the treaty trigger and includes the judgments of God.