The book of Revelation describes the people of God as sealed by God. Therefore, this great multitude of people belongs to God.
Revelation says that the redeemed bear a seal on their foreheads. The seal consists of the names of God and the Lamb and shows that the redeemed belong to God (Revelation 14:1). The seal is presumably not a visible one but a way of indicating that people find their identity in relationship to God and Christ. This seal or relationship does not mean that people are exempt from all earthly suffering, but it does show that God has claimed them and gives them the promise of life everlasting. John hears that those who are sealed number 144,000 from the 12 tribes of IsraelThe patriarch Jacob fathered twelve sons who became the ancestors the Twelve Tribes of Israel. Divisive political conditions led to a separation of these united tribes into the Northern and Southern Kingdoms after the death of Solomon in 931 B.C.E More (7:4), but when he turns to look at them he discovers that they are actually a countless multitude from every tribe and nation (7:9). The 144,000 are not a special ethnic group. The imagery describes the whole people of God. The seal that they bear is the opposite of the mark of the beast, which is introduced in Revelation 13:11-18.