The prologue to the Epistle to the Hebrews (1:1–4) is one of a handful of such texts (cf. John 1:1-18; 1John 1:1–4; Ephesians 1:1–14; Colossians 1:15–23) that speak of the pre-existence of Christ, and on that score alone it should be regarded as a deep, clear source that invites repeated, even continual, contemplation. It also lends such rich and vital literary context to what follows that it really should be included in any exposition of these subsequent verses (1:13—2:4). Since we are focusing, however, on material excluded from RCL, we take up with the conclusion of the supra-angelic excursus (1:5–14), where a final proof text (1:13) is cited to support the apostle's assertion that the Son of God (and his name) is immeasurably superior to the angels (and their names) (1:4). This final proof text is particularly significant, hence, its position as a rhetorical coup de grâce (and hence the inexplicability of its exclusion from RCL), in that it speaks not only of the Son's relationship to the Father (or in the original psalm setting, the LORD), but of his enthronement at the right hand of the LORD, elsewhere "the right hand of power" (Matthew 26:64); moreover, the chosen verse is taken from a psalm that testifies to this favored one's priestly role according to a new, yet pre-existent (non-Levitical) order, the order of Melchizedek (Psalm 110; see also First Sunday of Christmas). This priestly role will be the focus of a lengthy exposition in Hebrews 4—10. Here, however, the seating of the Messianic Son, with his enemies converted (comically) into a footstool, clearly refers to the "rest," or the sitting down, of the Son of God after his great work whereby he "made purification for sins" (v. 3).
By this work of purification, we mean, of course, no merely human labor or mundane task among many others, but the central work of redemption history, "the" work on which absolutely everything— every hope of salvation, renewal, restoration, reconciliation, the continuation of life itself—depends. Thus, where the prologue speaks of God's revelation through the Son, the Son's sovereign appointment as "heir of all things," his mediating role in creation, his glorious character, his equality with God, his power to sustain all things, his great work of purification, his incomparable superiority to the angels, and his heavenly enthronement, the conclusion of the excursus (1:13–14) and the summons to "pay greater attention" clearly assert that what is at stake in our doing so, in our attending to the revealing word and the atoning work of Christ, is our very salvation, the salvation in the service of which the angels themselves labor (v. 14). So "great" is this salvation that, were we to "drift away from it" (2:1), forget or "neglect" it, there would be no escape (2:3). Threatening as this may seem, the logic is as simple and straightforward as possible: how can one escape when one refuses the only means of escape? And if anyone is in doubt as to the greatness and comprehensiveness of this salvific means of escape (i.e., the Son of God and his purifying work), the apostle assures us (or takes as an utterly reliable presupposition) that, according to this Christological (and perfectly logical) revelation and his atoning work, "every transgression (and) disobedience (have) received a just penalty" (2:2). What incomparably good news!
As for the certainty and reliability of all this, we are reminded that this is the message of God himself, who has not only spoken it (1:1) through various messengers, but also attested to it by way of additional "signs and wonders and various miracles, and by gifts of the Holy Spirit" (2:4). This means of escalating divine authority and assurance will be mentioned again very explicitly when the epistle speaks of God's sworn promise to Abraham (6:13). Though less explicit here, the same (at very least) doubling of the divine assurance is clearly indicated: the revelation of salvation comes from no less than God himself, and God himself has sworn to it repeatedly. With so much at stake then, and with such unimpeachable solid ground on which to trust it, the demand for "greater attention" on our part is—or it should be—absolutely riveting.