They are firstfruit jews as it explicitly states.
That's why Paul used the word "firstfruits" in 1 Cor 15:23 in RELATION to receiving a glorified body.
The other uses of "firstfruits" is NOT related to receiving a glorified body.
The real emphasis is on the resurrection where all saved people will receive their glorified body. Not on being second in line for receiving a glorified body, plus the fantasy of this assumed journey up to heaven, which the Bible says NOTHING about.
And the Bible specifically says there is ONE resurrection (reception of glorified bodies).
So those pretribbers who argue that there are "waves" or "stages" or "series" of resurrections where believers will receive their resurrection bodies are flatly wrong.