Those priests - The Levitical, were made without an oath, to show that the whole system was changeable, and might be abolished.
But this - The everlasting priesthood of Christ, with an oath, to show that the Gospel dispensation should never change, and never be abolished.
By him - God the Father, that said unto him - the promised Messiah, Psalm 110:4, The Lord sware, to show the immutability of his counsel, and will not repent - can never change his mind nor purpose, Thou art a priest for ever - as long as time shall run, and the generations of men be continued on earth. Till the necessity of the mediatorial kingdom be superseded by the fixed state of eternity, till this kingdom be delivered up unto the Father, and God shall be all in all, shall this priesthood of Christ endure.
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. The word rendered “oath” is in the margin “swearing of an oath.” This is the proper meaning of the Greek word, but the sense is not materially varied.
But this with an oath - This priest, the Lord Jesus, became a priest in virtue of an oath.
And will not repent - That is, “will not regret, or will not alter his mind through regret” - for this is the meaning of the Greek word.