Their explanation is seriously flawed. The new covenant is concluded with God's new nation, called the Israel of God (Hebr. 8:8, 9; cf. Jer. 31:31). Now, who is the Israel of God? According to them it's the 144,000. But according to the following scriptures, the 144,000 make up only part of Israel.
15 For neither is circumcision anything nor is uncircumcision, but a new creation [is something].
16 And all those who will walk orderly by this rule of conduct, upon them be peace and mercy, even upon the Israel of God. (Gal. 6:15, 16 NWT)
Everybody must follow this "rule of conduct."
And I heard the number of those who were sealed, a hundred and forty-four thousand, sealed out of every tribe of the sons of Israel, (Rev. 7:4 NWT)
The 144,000 come from Israel. Who then, is the twelve tribes of Israel? Must be the whole congregation ("church").
Jesus said to them, Truly I say to YOU, In the re-creation, when the Son of man sits down upon his glorious throne, YOU who have followed me will also yourselves sit upon twelve thrones, judging the twelve tribes of Israel. (Matt. 19:28 NWT)
They will govern the twelve tribes of Israel. 1) They cannot be Israel and govern over Israel in this instance. 2) The new covenant involves all Israel and not only the 144,000. 3) This is a permanent covenant which will carry on even after the 144,000 have been recalled to heaven.
Where's Scholar when you need him? I would dearly love to hear his explanation.