21. “But this,” i.e., Christ, “with an oath.” The words, “the Lord hath sworn and he will not repent,” are the words of the Psalmist, and not of God, as their collocation in this verse would imply, “Thou art a priest for ever.” In some Greek copies are added the words, according to the order of Melchisedech. Griesbach doubts their authenticity.
Hebrews 7:21