John Chrysostom, on Heb 8:1

Paul mixes the lowly things with the lofty, ever imitating his Master, so that the lowly become the path to the lofty, and through the former we are led to the latter, and when we are amid the great things we learn that these lowly ones were a condescension. This accordingly he does here also. After declaring that "He offered up Himself," and showing Him to be a "High Priest," what does he say? "Now of the things which we have spoken this is the sum: we have such an High Priest who is set down on the right hand of the throne of the majesty." And yet this is not the office of a Priest, but of Him whom the Priest should serve.

"A minister of the sanctuary," not simply a minister, but "a minister of the sanctuary. And of the true Tabernacle, which the Lord pitched and not man." Thou seest the condescension. Did he not a little before make a separation, saying: "Are they not all ministering spirits?" (supra, i. 14) and therefore (he says) it is not said to them, "Sit thou on my right hand," (supra, i. 13) for He that sitteth is not a minister. How is it then that it is here said, "a minister," and "a minister of the Sanctuary"? for he means here the Tabernacle.

See how he raised up the minds of the believing Jews. For as they would be apt to imagine that we have no such tabernacle as they had, see here (he says) is the Priest, Great, yea, much greater than the other, and who has offered a more wonderful sacrifice. But is not all this mere talk? is it not a boast, and merely said to win over our minds? on this account he established it first from the oath, and afterwards also from "the tabernacle." For this difference too was manifest: but the Apostle thinks of another also, "which" (he says) "the Lord pitched [or "made firm"] and not man." Where are they who say that the heaven whirls around? where are they who declare that it is spherical? for both of these notions are overthrown here.

"Now" (he says) "of the things which we have spoken this is the sum." By "the sum" is always meant what is most important. Again he brings down his discourse; having said what is lofty, henceforward he speaks fearlessly.