According to John, the named writer of Revelation:
They were were the servants of our God (Rev. 7:3).
They were 12,000 from each from every tribe of the sons of Israel (Rev. 7:5-8).
They were virgins (Rev. 14:4).
They were redeemed from the earth (Rev. 14:3); redeemed from mankind as first fruits (Rev. 14:4).
They told no lie; they were blameless (Rev. 14:5).
They were sealed with the name of the Father on their foreheads (Rev. 7:3).
They have their tribe names inscribed on the gates of the holy city Jerusalem coming down from heaven (Rev. 21:12).
The author has seen the salvation of remnant Jews, a remnant, “from all the tribes of Israel”, Rev. 7:4.
Are they representatives of Gentiles servants of God too?
No. John said in Rev. 7:9, after that vision of the 144,000, he beheld,
“a great multitude that no one could number, from every nation, from all tribes and peoples and languages….clothed in white robes, with palm branches in their hands.”
The Greek word used to describe the innumerable multitude is “ethnos” which is also translated as “Gentiles” elsewhere.
According to Rev. 7:15, they serve God “day and night.” That makes them God’s servants too.
In other words, aside from the remnant Israelites that John saw, he has also seen the salvation of innumerable multitude from every nations.
While the 144,000 remnant of Jews were on Mt. Zion (Rev. 14:1), a great multitude of non-Jewish nations were in a heavenly Temple, singing praises and salvation songs (Rev. 19:1,6-8) and worshiping God on his throne (Rev. 7:11, 15).
Keep Calm, Don’t ‘Herme-new-twist’
So, don’t worry if the text doesn’t seem to say you belong to the 144,000 especially if you’re not a Jew. You don’t have to argue non-sequitur to make yourself belong to a remnant.
Learn from the mistake of Kevin DeYoung when argued non-sequitur in favor of his Anti-premillennial bias in his blog in TGC.
You don’t have to make Revelation say what it is not actually saying. Aside from those 144,000 there were also a great innumerable multitudes clothed in white, clean, washed with the blood of the Lamb. Even chapter 7, John saw a vision of Gospel preaching, “to every nation, and kindred, and tongue, and people,” Rev. 14:6.
Lastly, Revelation doesn’t have to say that those innumerable great multitudes were sealed to be saved too. They already praise God and they were singing salvation songs to him in his temple, and more importantly Rev. 7:17 says, “the Lamb in the midst of the throne will be their shepherd, and he will guide them to springs of living water, and God will wipe away every tear from their eyes.”