Hebrews 10:12

But this man, after he had offered one sacrifice for sins for ever, sat down on the right hand of God;

This man - emphatic (Hebrews 3:3).

Forever - join with "offered one sacrifice;" namely, the efficacy of which endures forever [ eis (G1519) to (G3588) dieenekes (G1336): continuously] (cf. Hebrews 10:14). The mass, which professes to be the frequent repetition of one and the same sacrifice of Christ's body, is hence disproved. For not only is Christ's body one, but also His offering is one, and past [ prosenengkas (G4374): aorist, not action continued down to the present, as the perfect], and inseparable from His suffering (Hebrews 9:26). The mass is as opposed to Paul's view of Christ's ONE finished sacrifice, as the Jewish sacrifices would be now. A repetition would imply that the once for-all offering was imperfect, and so would be dishonouring to it (Hebrews 10:2; Hebrews 10:18). Hebrews 10:14, on the contrary, says, "He hath PERFECTED FOREVER them that are sanctified." If Christ offered Himself at the last supper, then He offered Himself again on the cross, and there would be two offerings; but Paul says there was only one, once for all (note, Hebrews 9:26). Usage in this letter puts [ eis (G1519) to (G3588) dieenekes (G1336)] "forever" after, not before, that which it qualifies (Hebrews 10:1; Hebrews 10:14; Hebrews 7:3).

Also, "one sacrifice ... forever," stands in contrast to "oftentimes the same sacrifices" (Hebrews 10:11). Also, 1 Corinthians 15:23; 1 Corinthians 15:28, agrees with Hebrews 10:12; not joining, as Alford, "forever" with "sat down;" for Jesus is to give up the Mediatorial throne 'when all things shall be subdued unto Him,' and not to sit on it forever. Leviticus 16:17 (cf. Hebrews 4:13) shows that on the day of atonement none but the high priest could offer a sin offering for the people, until he came out of the Holiest, having finished his? Christ, our High Priest, having gone within the heavenly veil, and not yet come out, precludes any other from priestly ministry during our whole dispensation, which is our day of atonement and year of jubilee (Leviticus 25:9). His ascension into heaven is necessary to His priesthood: 'if on earth, He would not be a priest;' much less are His disciples (Hebrews 8:4).