but this one was made a priest with an oath by the one who said to him: “The Lord has sworn and will not change his mind, ‘You are a priest forever.’”
Observe the necessity there was of raising up another priest, after the order of Melchisedec and not after the order of Aaron, by whom that perfection should come which could not come by the Levitical priesthood, which therefore must be changed, and the whole economy with it, Heb 7:11, Heb 7:12, etc. Here, I. It is asserted that perfection could not come by the Levitical priesthood and the law.
Commenting on Hebrews 7:11-28
By so much was Jesus made a surety of a better testament. Or "covenant", for the word signifies both; and what is intended may be called both a testament and a covenant; a testament, because it is founded in the good will and pleasure of God, and respects an inheritance bequeathed by God the Father to his children, which was confirmed and comes to them...
Verse 21. For those priests were made without an oath. The Levitical priests were set apart and consecrated without their office being confirmed to them by an oath on the part of God. They received it by regular descent, and when they arrived at a suitable age they entered on it of course. Jesus received his office by special appointment, and it was secured to him by an oath.