Why would Hebrews pick it up then? IOW, if very early Christians understood Haggai to refer only to a physical temple, rather than the spiritual one (us), why this then?
Hag. 2:6 For thus saith the LORD of hosts; Yet once, it [is] a little while, and I will shake the heavens, and the earth, and the sea, and the dry [land];
Which Paul (in Hebrews) picks up:
Heb. 12:26 Whose voice then shook the earth: but now he hath promised, saying, Yet once more I shake not the earth only, but also heaven.
v27 And this [word], Yet once more, signifieth the removing of those things that are shaken, as of things that are made, that those things which cannot be shaken may remain.
The physical temple was destroyed (shaken), but not the spiritual one, which is to what's referred.
I think there is more to it than that. What Paul was talking about was not simply the Temple being removed, but the whole Old Covenant earthly "kingdom" being removed so that the New Covenant heavenly "kingdom" might remain.
"And this word, Yet once more, signifieth the removing of those things that are shaken, as of things that are made, that those things which cannot be shaken may remain. Wherefore we receiving
a kingdom which cannot be moved, let us have grace ..." Hebrews 12:28
This was the context of Haggai 2, that the Lord would "shake" the heavens and the earth, so that the Old Covenant kingdom might be removed, which was speaking of God's earthly kingdom, which was Israel. That "kingdom" was "removed" because the heavenly kingdom, the Kingdom of God, which cannot be shaken or moved, had come, signified by the veil in the Temple being rent showing that the way into the presence of God had been opened.
This "shaking" of the earthly Kingdom of David and it being removed is graphically foretold in a number of other prophecies you are probably familiar with. The "fig tree" being "shaken by a mighty wind," is another illusion to this removing of the Jewish commonwealth after the coming of the Kingdom of God. That "mighty wind" was a reference to the outpouring of the Holy Ghost, which is described on the Day of Pentecost: "And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting. And there appeared unto them cloven tongues of fire ..." Acts 2:2-3
So this prophecy of Haggai, which Paul quotes in Hebrews, spoke not just of the earthly Temple being shaken and being removed, but it was speaking in a broader context of the entire Kingdom of Israel being shaken and removed, while the Kingdom of God, which can never be shaken, would remain, forever.
Standing Up, an interesting sidenote, the name of the second goat offered on the day of Atonement, "for Azazel," literally means "for removing." The first goat, the one "for Jehovah," represented Christ, because that goat was sacrificed in the Temple and it's blood was carried into the Holiest and sprinkled on the Mercy Seat and on all the furnishing and vessels of the Temple and then finally on the people to cleanse them of sin. That goat represented the Jews who believed in Jesus and their sins were atoned by the sprinkling of his blood. But the other goat, the one "for Azazel," (for removing) represented those Jews who refused the Gospel, refused the atoning blood of Jesus. Their sins rested on their own heads, and like that generation that did not have faith and their carcases fell in the wilderness and they never entered the promised land, the Jews who refused the Gospel bore their sins upon their own heads and they were "removed," and they perished "in the wilderness" without ever entering God's Kingdom.
But that is what Paul was referring to in Hebrews 12, the old earthly kingdom, which was a type and a shadow, having been fulfilled it was removed and the new heavenly kingdom, which is eternal and can never be moved, remains.
In Christ,
Pilgrimer