Hebrews 7:15-18 And it is yet far more evident: for that after the similitude of Melchisedec there arose another priest, Who is made, not after the law of a carnal commandment, but after the power of an endless life. For he testified, Thou are a priest for ever after the order of Melchisedec. For there is verily a disannulling of the commandment going before for the weakness and unprofitableness thereof. 

‘And it is yet far more evident: for that after the similitude of Melchisedec there arose another priest.’ It is more abundantly manifest [Greek: katadelos] very plain; that God designed the Levitical priesthood to be changed, because of the oath in Psalms 110:1-7 which declares the Messiah should be a priest after the order of Melchizedek who was not only a priest but also a prophet and a king (7:1-10). None of the Levitical priests exercised a double or a triple office, as was manifest in Jesus Christ.

‘Carnal’ [Greek: sarkines] fleshly; natural; human (7:16; Rom. 7:14; 15:27; 1Cor. 3:1-4; 9:11; 2Cor. 10:4). Here it means the full depravity of fallen man, sold as a slave and under the control of animal appetites and the forces of evil spirits. The word carnal does not always mean sinful or corrupt, but sometimes feeble, frail, or human. The idea here is that Christ was not appointed a priest after the order of Aaron wherein weak and perishing men must succeed each other, but He was made a High Priest after another order – after the power of immortality or endless life (7:16-17).

‘Thou are a priest for ever after the order of Melchisedec.’ This is the 17th Old Testament prophecy in Hebrews (7:17; Ps. 110:4).

‘Disannulling’ [Greek: athetesis] abolition, rejection. Translated as “disannulling” (7:18) and “put away” (9:26). What was disannulled? Not only the commandment of Hebrews 7:16-18 concerning the priesthood but all the law, including the Ten Commandments. That the commandment here refers to the law is made clear in Hebrews 7:19.

Fifteen things the Law was unprofitable in Redemption from sin (9:15; 10:1-18). Making perfect (7:19; 10:1). Giving eternal inheritance (Rom. 4:13). Freeing from sin and death (Rom. 8:2-3). Imparting faith (Gal. 3:12). Giving life (2Cor. 3:7; Gal. 3:21). Purging the conscience (9:9; 10:1-4). Working miracles (7:18; Rom. 8:3). Giving access to God (9:7-8; 10:19-23). Giving mercy (10:28). Justification (Gal. 2:16; Rom. 4:1-25). Imparting righteousness (Rom. 3:21-25). Imparting the Spirit (Gal. 3:1-5, 14). Providing realities (Col. 2:14-17; 8:5; 10:1). Sanctification (10:9-14).