Throughout his letter, he contrasts the person and work of Christ with various good persons and institutions — angels, Moses, Aaronic priesthood, Mosaic covenant. Here in chapter 10, he is focusing on the whole ritual surrounding the sacrifices offered by the Aaronic priesthood. Focus on the first verse of chapter 10, and see how many ways he finds to contrast its limited and temporary effects with the perfect and final sacrifice of Christ, in one verse:
Σκιὰν γὰρ ἔχων ὁ νόμος τῶν μελλόντων ἀγαθῶνThen focus on vv. 11-13—
οὐκ αὐτὴν τὴν εἰκόνα τῶν πραγμάτων
ταῖς αὐταῖς θυσίαις
εἰς τὸ διηνεκὲς
τοὺς προσερχομένους τελειῶσαι·
Καὶ πᾶς μὲν ἱερεὺς ἕστηκεν καθ᾽ ἡμέραν λειτουργῶν καὶ τὰς αὐτὰς πολλάκις προσφέρων θυσίας, αἵτινες οὐδέποτε δύνανται περιελεῖν ἁμαρτίας, 12 οὗτος δὲ μίαν ὑπὲρ ἁμαρτιῶν προσενέγκας θυσίαν εἰς τὸ διηνεκὲς ἐκάθισεν ἐν δεξιᾷ τοῦ θεοῦ, 13 τὸ λοιπὸν ἐκδεχόμενος ἕως τεθῶσιν οἱ ἐχθροὶ αὐτοῦ ὑποπόδιον τῶν ποδῶν αὐτοῦ. 14 μιᾷ γὰρ προσφορᾷ τετελείωκεν εἰς τὸ διηνεκὲς τοὺς ἁγιαζομένους.The passage is a marvel. See how he pounds his point again and again, just in v. 11. It isn't some priests, it's πᾶς ἱερεὺς. Every priest ἕστηκεν, for he can can never sit, for his work is never finished. The work is carried on not just occasionally, but καθ᾽ ἡμέραν. It wasn't a single event, but it was ongoing (λειτουργῶν, προσφέρων—present participles). Nor does he try different measures, but offers τὰς αὐτὰς. Nor can he ever do it once and be done with it, but must offer them πολλάκις.
Why is that? Because these sacrifices are the very ones (αἵτινες) that not only don't take away sins, but are incapable of (δύνανται) taking away sins; and that not only on occasion, but regularly (present tense); and that not only at one time, but not at any time (οὐδέποτε).
You could make a column, then, and contrast each of these points with what he then asserts about Christ's sacrifice. He was a different Person (οὗτος); His sacrifice wasn't πολλάκις, but μίαν; its effect wasn't temporary and partial but εἰς τὸ διηνεκὲς; He did not continue to stand making this sacrifice, but ἐκάθισεν; His seat was not on a chair in an earthly tabernacle, but ἐν δεξιᾷ τοῦ θεοῦ.
And all that is why, while centuries of Mosaic sacrifices οὐδέποτε δύναται τοὺς προσερχομένους τελειῶσαι (v. 1), by starkest contrast the one sacrifice of Jesus τετελείωκεν εἰς τὸ διηνεκὲς τοὺς ἁγιαζομένους (v. 14).
This is one of those passages that, to me, is difficult to preach, because one despairs ever of communicating the grandeur of the author's teaching. He has said it so eloquently, emphatically, and concisely. Our danger is that we will either blunt it and bury it beneath a flood of words, or fail ever to scale the peak and capture the lofty truth he communicates.