8.2 – καὶ τῆς σκηνῆς τῆς ἀληθινῆς, “of the true tabernacle” is a polemical phrase that points ahead to 8.5-6, with its argument that the Mosaic tabernacle (and thus also the 2nd Temple refurbished by Herod) is a copy of a heavenly original.
The effect of this argument is to turn one of the early Christians’ weak points – the absence of Christ from present view on this earth – into a point of superiority to Judaism. Why is Christ not here and visible like the Aaronite priests? Because He has ascended into heaven to do His ministry in the only Temple that really matters. The vaunted temple in Jerusalem is not the true one; is it not then a false one? And worse, it is a σκηνή set up (“pegged”) by men, not God.
The Jerusalem temple’s divine authorization was a weak point for Christians, who expected its demise, but could not help admitting that it had been instituted by God. Here, Hebrews makes a clever move by shifting the question from the Temple’s institution to its construction. This, of course, was elaborately narrated in Israel’s scriptures, both for the Mosaic tabernacle in Exodus 36-39, and for the Temple built by Solomon in 1 Kings 5-8 (and rebuilt in Ezra 3-6). Thus, the fact that God commanded the construction of the Temple is rhetorically undercut by the equally undeniable fact that He did not Himself construct it.
This argument is formally similar to Paul’s dismissal of circumcision as “made in the flesh with hands” in Eph. 2.11. Circumcision too was instituted by God, but human hands executed it no less than they constructed the Temple. And in the same way, the pejorative λεγομένης (“so-called circumcision”) parallels the use of ἀληθινῆς in Hebrews 8.2 to imply that the present temple in Jerusalem is not the true one.
8.4 – εἰ μὲν οὖν ἦν ἐπὶ γῆς – note the contrafactual conditional with its imperfect present-unreal verb. If Jesus were here (but He is not), then He would not be a priest. He is thus removed not only from actual rivalry with the Aaronite priests (since He is not ἐπὶ γῆς and they are), but also from even hypothetical competition with them: even if He were ἐπὶ γῆς, He would not have any need to perform the sort of work that they do, since He is not concerned with serving a “copy and shadow” (8.5).
Again, this defangs a powerful argument of unbelieving Judaism: namely, the observable presence of very visible Aaronite priests going about their divinely commanded work in the solid Herodian temple. “Where is your priest? What Temple does He work in?” The pressure of this argument on early Judaeo-Christians would have been powerful. The author of Hebrews brilliantly turns it against the Jewish opponent: the very immanence of that temple, the very repetition of those rituals, the very visibility of those priests are all proof that that entire system is ineffective and inferior. If Jesus is not visible, it is because His priesthood truly qualifies Him to enter the only Temple that really matters, with the only sacrifice that is permanently effective.