Hebrews 7:18-21

For, on the one hand, a former commandment is cancelled because of its weakness and uselessness [because of its inability to justify the sinner before God] (for the Law never made anything perfect); while on the other hand a better hope is introduced through which we now continually draw near to God. And indeed it was not without the taking of an oath [that Christ was made priest] (for those Levites who formerly became priests [received their office] without [its being confirmed by the taking of] an oath, but this One [was designated] with an oath through the One who said to Him, “THE LORD HAS SWORN AND WILL NOT CHANGE HIS MIND or REGRET IT, ‘YOU (Christ) ARE A PRIEST FOREVER’ ”). [Ps 110:4]