And they truly were many priests, because they were not allowed to continue by reason of death:
All Commentaries on Hebrews 7:23 Go To Hebrews 7
George Leo Haydock
AD 1849
Many priests The apostle notes this difference between the high priests of the law, and our high priest, Jesus Christ: that they being removed by death, made way for their successors: whereas our Lord Jesus is a priest for ever, and hath no successor; but liveth and concurreth for ever with his ministers, the priests of the New Testament, in all their functions. Secondly, that no one priest of the law, not all of them together, could offer that absolute sacrifice of everlasting redemption, which our one high priest, Jesus Christ, has offered once and for ever. (Challoner)