In the beginning, the Watchtower said that the great crowd was seen in courtyard of the gentiles of the temple. But this statement is clearly dishonest, because the sanctuary (NAOS), where the great crowd is seen in Rev 7:15, can't represent a courtyard, because the sanctuary was the inner place of the temple only for priests. This fact already destroys the Watchtower's argument that ony the 144000 are priests. So, in 2002 year, the Watchtower had to invent a "new light", admitting that the great crowd can't be in the courtyard:
In times past, it has been said that the great crowd is in a spiritual equivalent, or an antitype, of the Court of the Gentiles that existed in Jesus’ day. However, further research has revealed at least five reasons why that is not so. (w02 5/1, "Question for readers")
So, the Watchtower, in the same article had to place the John's vision of the temple, not related to the Herod's temple, but in the Solomon temple. However, for the Solomon's temple, the Septuagint used the greek word NAOS for the HEKAL (read 2 Chr 3:17), which was the inner place of the temple only for jews. Were not the 144000 the only spiritual christian jews according to the Watchtower teaching?. Furthermore, in Psalm 11:4 the Septuagint reads "The Lord is in his holy NAOS, in heaven is his throne". So, it is clear that the NAOS of God in Rev 7:15 is in heaven, so the Watchtower's argument does not work.