A.T. Robertson Commentary Hebrews 5:6

"as he saith also in another [place,] Thou art a priest for ever After the order of Melchizedek." — Hebrews 5:6 (ASV)

In another place (εν ετερω). That is Ps 110:4. It is this crucial passage by which the author will prove the superiority of Jesus to Aaron as high priest. Only the word priest (ιερευς) occurs here which the author uses as synonymous with high priest (αρχιερευς). The point lies in the meaning of the phrase "After the order of Melchizedek" (κατα την ταξιν Μελχισεδεκ). But at this point the only thing pressed is the fact of the divine appointment of Jesus as priest. He returns to this point (5:10-7:28).