The 144,000 are specifically mentioned only twice in the entirety of Scripture. In the end time, after God commands a temporary ceasing of calamities occurring on the earth (see Revelation 6), he sends an angel on a special mission. The angel is not to allow the sea, or trees (the entire earth) to be damage UNTIL a unique group of folks is first sealed.
4. And I heard the number of those who were sealed: one hundred forty-four thousand (144,000), sealed out of every tribe of the children of Israel (Revelation 7:2 - 4, HBFV throughout).
This group is mentioned again in Revelation 14, where it states the apostle John saw one hundred and forty-four thousand (144,000) which have God the Father's name on their foreheads (meaning they obey him and have His spirit in them, Revelation 14:1).
This special group of people in Revelation 7 are composed entirely of PHYSICAL descendants of Israel, as the Bible takes great pains to enumerate twelve tribes from which 12,000 people each will be converted (or sealed, see Revelation 7:5 - 8).
Two Israelite tribes are not specifically listed in Revelation 7. The first missing tribe is Dan (see our article on why Dan might have been left out). The second missing tribe is Ephraim. The Bible does not state why Ephraim, one of Joseph's two sons, is not directly named as contributing toward the 144,000. His other son Manasseh is listed in the chapter (verse 6). It is possible that the people of Ephraim are "hidden" within the distinct naming of the tribe of Joseph (verse 8).
When are the 144,000 sealed (a spiritual mark to denote their conversion, a possible allusion to Ezekiel 9:4) by a mighty angel? How does their sealing fit into prophetic end time events? After a great martyrdom of saints instigated by the Satan-inspired one world government, God will cause signs to appear in the heavens (Revelation 6:12 - 14). It is AFTER these signs, and just BEFORE the prophetic "Day of the Lord" that 144,000 descendants of Israel and "a great multitude" from around the world become converted (Revelation 7).
The 144,000 are unconverted physical descendants of Israel who repent and become Christians near the middle of the Great Tribulation period. At the start of this time of global trial and trouble (Matthew 24) they are NOT Christians. If they were, they would have either been taken to a "place of safety" (1Thessalonians 4:16 - 17, Revelation 12:6) or would have been martyred for their faith. This means that any Christians living today are not and will not be a part of this select group! The 144,000 are part of, but not the entirety, of God's church who will be changed into spirit beings at the return of Christ (Revelation 5:10).