Jamieson, Fausset and Brown on Hebrews 7:28

28. For--reason for the difference stated in He 7:27, between His one sacrifice and their oft repeated sacrifices, namely, because of His entire freedom from the sinful infirmity to which they are subject. He needed not, as they, to offer For His own sin; and being now exempt from death and "perfected for evermore," He needs not to REPEAT His sacrifice.

the word--"the word" confirmed by "the oath."

which--which oath was after the law, namely, in Psa 110:4, abrogating the preceding law-priesthood.

the Son--contrasted with "men."

consecrated--Greek, "made perfect" once for all, as in He 2:10; 5:9; see on He 2:10; He 5:9. Opposed to "having infirmity." Consecrated as a perfected priest by His perfected sacrifice, and consequent anointing and exaltation to the right hand of the Father.