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.
The Lord sware - see the note at Hebrews 6:13. The reference here is to Psalms 110:4. “The Lord hath sworn.”
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.