DA, A Biblical Defense of Catholicism, pp. 69-70:
The theme of the Epistle to the Hebrews is Christ as our High Priest. As such, the “priestly” verses are very numerous (for example, 2:17, 3:1, 4:14-16, 5:1-10, 6:20, 7:1-28, 8:1-6, 9:11-15, 24-28, 10:19-22). The teaching here acquires much more meaning within Catholic Eucharistic theology, whereas, in evangelical, non-sacramental Protestant interpretation, it is necessarily “spiritualized” away. For nearly all Protestants, Jesus Christ is a Priest only insofar as He dies sacrificially as the “Lamb” and does away with the Old Testament notion of animal sacrifice. This is not false but it is a partial truth. Generally speaking, for the Catholic, there is much more of a sense of the ever-present Sacrifice of Calvary, due to the nature of the Mass, rather than considering the Cross a past even alone.
In light of the repeated references in Hebrews to Melchizedek as the prototype of Christ’s priesthood (5:6,10, 6:20, 7:1-3,17,20), it follows that this priesthood is perpetual (for ever), not one time only. For no one would say, for example, that Christ is King (present tense) if in fact He were only King for a short while in the past. This (Catholic) interpretation is borne out by explicit evidence in Hebrews 7:24-25:
He holds his priesthood permanently, because he continues for ever. Consequently he is able for all time to save those who draw near to God through him, since he always lives to make intercession for them.
If Jesus perpetually intercedes for us, why should He not also permanently present Himself as Sacrifice to His Father? The connecting word, consequently, appears to affirm this scenario. The very notion, fundamental to all strains of Christian theology, that the Cross and the Blood are efficacious here and now for the redemption of sinners, presupposes a dimension of “presentness” to the Atonement.
Granting that premise, it only remains to deny that God could, would, or should truly and actually re-present this one Sacrifice in the Mass. God certainly can do this, since He is omnipotent. He wills to do this because Jesus commanded the observance of the Lord’s Supper (Luke 22:19). Lastly, one can convincingly contend that He should do this in order to graphically “bring home” to Christians His Passion, Crucifixion, and Resurrection, and to impart grace in a real and profound way in Communion. The One Propitiatory Atonement of Calvary is a past event, but the appropriation of its spiritual benefits to Christians is an ongoing process, in which the Mass plays a central role.
The Sacrifice of the Mass, like the Real Presence in the Eucharist, is an extension of the Incarnation. Accordingly, there is no rational a priori objection (under monotheistic premises) to the concept of God transcending time and space in order to present Himself to His disciples. Nor is there any denying that the Sacrifice of Calvary is always present to God the Father and to Jesus Christ, God the Son. How then, can anyone deny that God could make the Cross sacramentally present to us as well?
James White, introductory exegetical comments prior to deeper exegesis of Hebrews 8:6ff.
The immediately preceding argument, leading to the key presentation of the new covenant in Heb. 8:6-13, flows from the identification of Christ with the superior priesthood of Melchizedek (Psalm 110:4, cited in Heb. 7:17, 21), leading to the description of Christ as the e;gguoj (guarantee/guarantor) of the new covenant, and also bringing the first use of krei,ttonoj diaqh,khj, better covenant, in 7:22, “so much the more also Jesus has become the guarantee of a better covenant.” Heb. 7:23-8:5 comprises a demonstration of the basis for the apologetic assertion that the new covenant is, in fact, a better covenant (part and parcel of the purpose of the letter), one that flows from the priestly nature of Christ’s work. 7:23-25 proves this by the contrast of the mortal priests with the one priest, Jesus Christ; and 7:26-28 does so in light of the sinfulness of the many priests and hence their repeated sacrifices versus the singular sacrifice of the innocent, undefiled Christ. 8:1-6, then, provides first a summary statement of the preceding arguments (i.e., our one high priest has entered into the heavenlies) and then provides the thesis statement for the description of the superiority of the new covenant from Jeremiah 31 with the assertion that Christ has obtained “a more excellent ministry” than that of the old priests, that He is the mediator (in contrast, in context, to Moses, v. 5, Gal. 3:19, John 1:17) of a “better covenant” enacted on “better promises.” Some brief comments should be offered exegetically on these texts.
First, Christ’s role as singular and never dying high priest, and the resulting assurance of the perfection of His work, is seen by the writer as part of the demonstration of why the covenant of which He is the guarantee is “better” (7:23-25). While our English translations normally say something like, “The formerpriests existed in greater numbers” at 7:23, the literal reading is simply, “the priests,” contrasting the plural with the singular “he” (oi` vs. o`) in v. 24. The work of the many priests is, of necessity, imperfect, for they are “prevented by death” from “continuing” or “abiding.” But, in contrast, He “abides forever,” He is no longer subject to death. Hence, He, unlike the old priests under the old covenant, holds His priesthood (which has been shown to be superior in the preceding arguments) avpara,baton, permanently, or, in some sources, without successor. Both translations fit the context, for He never lays aside this priesthood, hence, it is “permanent” in contrast to the former priests. But likewise He has no successor in His office. The entire concept is meant to be in contrast to the old priests and their inherently temporary nature. As a result of the permanence of His priestly position, Christ has an ability the old priests did not possess. He is able to save. The profundity of the words may deflect proper attention. The permanence of His life and position as high priest grants to Him the ability to save. He is active in saving, and He is capable of so doing. As noted above, the soteriological content of the superiority of Christ’s work as high priest and of the new covenantcannot be dismissed or overlooked. The extent of His salvific work is noted by the phrase eivj to. pantele.j, which can be translated “forever” in the sense of permanence, or “to the uttermost” in the sense of completely, similar, in fact, to avpara,baton above. Owen noted the propriety of seeing both senses in the text:
Take the word in the first sense, and the meaning is, that he will not effect or work out this or that part of our salvation, do one thing or another that belongs unto it, and leave what remains unto ourselves or others; but “he is our Rock, and his work is perfect.” Whatever belongs unto our entire, complete salvation, he is able to effect it. The general notion of the most that are called Christians lies directly against this truth….That this salvation is durable, perpetual, eternal… and there is nothing hinders but that we may take the words in such a comprehensive sense as to include the meaning of both these interpretations. He is able to save completely as to all parts, fully as to all causes, and for ever in duration.
Just as the Father’s will for the Son revealed in John 6:38-39 demands perfection in His role as Savior, so too here the very same soteriological perfection and completion is central to the work of the eternal high priest. This is brought out with strong force in the rest of the verse, for the author indicates both the objectof the salvific work and the basis thereof, and both are intensely “priestly” statements. The singular priest saves “those who draw near to God through Him.” This clearly harkens back to the people who drew near in worship to God in the temple, and their representative, the high priest on the day of atonement. There is specificity to the salvific work of the priest. He does not make a general plan of salvation available, He saves a specific people (cf. Matt. 1:21). And secondly, “He always lives to make intercession for them” points to the same perfection of the high priest. His indestructible life means He never lays aside His priestly role, hence, since the high priest interceded (evntugca,nein, Rom 8:34) for those for whom He offered sacrifice, Christ ever lives to make intercession for those who draw near to God through Him, resulting in the perfection of their salvation. The work of intercession guarantees the salvation of a specific people in this passage. This is vital to remember as we look at the key text in Hebrews 8.
Similar themes appear in 7:26-28, including the perfect character of the high priest (v. 26), which establishes another element of His supremacy over the old priests, for He does not have to offer sacrifice for His own sins, and then the sins of the people. But here also appears a concept that will be expanded upon greatly at a later point, for the author says, “because this He did once for all when He offered up Himself.” Self-offering is yet another aspect of what sets the priesthood of Christ apart, for obvious reasons, from the priesthood of old. The high priest presents the offering in His own body, a concept expanded upon in chapter nine. But He did so “once for all.” The sacrifice is a singularity in time, for the author uses the temporal adverb, evfa,pax, to strongly emphasize this concept. The old priests sacrificed often for themselves, while Christ offered one sacrifice (Himself) for the people.
 e;gguoj is a hapax legomena in the NT, appearing only in the Apocryphal books of Sirach and 2 Maccabees prior to this. It has semantic connections to avrrabw.n (down payment) in Eph. 1:14, for in common secular usage it refers to providing security or a guarantee, normally in a financial or business transaction. The guarantee then of the better covenant is introduced here within the context of Christ’s superior priesthood, His indestructible life, and divine ability to save to the uttermost (7:24-35).
 Using the common me.n/de. form translated “on the one hand/on the other hand.”
 o[qen, “for which reason.”
 John Owen, An Exposition of the Epistle to the Hebrews, Hebrews 6:1-7:28, in The Works of John Owen, William Goold, ed. (Ages Digital Library, 2000), pp. 646-647.