For whatever else might be derived from Rev 7, the twelve tribes listed and the 12,000 "out of" each tribe represent a return to what initially would have been the case in ancient Israel.
By saving the firstborn of Israel during the first Passover, God "bought" or purchased them. It was these "bought" ones that would have formed the priesthood. In their stead, and for practical reasons, Jehovah took the tribe of Levi to become the priestly tribe.
What Rev 7 portrays is a return to that original arrangement of priestly representatives from each tribe.
Interestingly, the 144,000 are portrayed in Rev 14 as "firstfruits," an agricultural term. Then Rev 14 depicts two more harvests. In verses 14-16 "one like a son of man" harvests "the harvest of the earth" which is "thoroghly ripe." Then in verses 17-20 another angel with a sickle harvests "the vine of the earth" which is ripe with badness and gets crushed in the "great winepress of the anger of God."
Now here is where it gets interesting. As you might know, the Society maintains that the "wheat" of the parable of the wheat and weeds refers only to the 144,000. This is pointed out in chapter 30 of the Rev Climax book. (pages 208-209) Then on page 213 the Society has an illustration of the two harvests mentioned in Rev 14:14-20. Both the good harvest and the bad harvest are pictured as bunches of grapes.
The 'good' harvest of verses 14-16 is described as "thoroughly ripe" (literally "dried out," xeraino Strong's #3583). Whereas, the 'bad' harvest is described as "ripe" (akmazo, Strong's # 187, which means "to flourish, be ripe, be in one's prime")
The word "ripe" for the 'bad' harvest perfectly describes plump grapes that are ready for harvesting. But the word "thoroughly ripe" used for the 'good' harvest in verse 15, if applied to grapes, means that they were ruined. "Thoroughly ripe" in verse 15 only makes sense if the crop being harvested was a grain crop like wheat or barley.
In other words, some sneaky New Yorkers have gone out of their way to try to make you think that only the 144,000 are of the "wheat."