Amplified: [Again, the former successive line of priests] was made up of many, because they were each prevented by death from continuing [perpetually in office]; (Amplified Bible - Lockman)
KJV: And they truly were many priests, because they were not suffered to continue by reason of death:
NLT: Another difference is that there were many priests under the old system. When one priest died, another had to take his place. (NLT - Tyndale House)
Wuest: And they indeed have been made many priests in number, because they were hindered from continuing by reason of death.
Young's Literal: and those indeed are many who have become priests, because by death they are hindered from remaining;
AND THE FORMER PRIESTS, ON THE ONE HAND, EXISTED IN GREATER NUMBERS BECAUSE THEY WERE PREVENTED BY DEATH FROM CONTINUING: kai oi men pleiones eisin (3PPAI) gegonotes (RAPMPN) hiereis dia to thanato koluesthai (PPN) paramenein (PAN): (Heb 7:8; 1Chronicles 6:3-14; Nehemiah 12:10,11)
Priest (hiereus from hieros = sacred) is a sacred person serving at God’s altar. There were 24 classes for the service of the temple (see 1Chr 24). Compare to Webster's definition of pontifex [Latin pontific-, pontifex, from pont-, pons bridge + facere to make — more at find, do] which is literally one who makes a bridge! Spanning the gap between God and man caused by man's sin.
As if to picture that the Levitical priesthood would never be able to bring them to salvation, God gave Israel a dramatic and significant demonstration, recorded in Nu 20:23-29. When Aaron, the first high priest and progenitor of all succeeding priests, was about to die, God commanded Moses to bring Aaron and his son and successor, Eleazar, to Mount Hor, in view of all the people. Aaron’s high priestly garments were taken from him and placed on Eleazar. After Aaron died, the people mourned for him for 30 days. The people’s attention was specially focused on Aaron’s death, as if God were impressing upon them the fact that the priesthood he represented was a dying priesthood.
In this brief demonstration, along with Moses’ own death shortly afterward, two things about the Old Covenant were symbolized: it was not permanent, and it could not bring the people into the Promised Land. It was temporary and it could not save. Neither the law (represented by Moses) nor the sacrifices (represented by Aaron) could deliver from the wilderness of sin and bring into the land of salvation.
Wuest on prevented by death from continuing - Another proof of the superiority of the New Testament over the First Testament is found in the continued life of the priest, this priest therefore able to make intercession for the believer forever, and thus able to save him completely, whereas the Aaronic priests were compelled by death to transfer their ministry to the next priest in succession. The word “continue” is the translation of parameno which means “to remain alongside.” The idea is that because the Aaronic priests died, they were hindered from abiding by their ministration. (Hebrews Commentary online)
Spurgeon - A common priest served from thirty to fifty years of age, and then his work was done. Priests of the house of Aaron, who became high priests, held their office through life. Sometimes a high priest would continue in his office, therefore, for a considerable length of time, but in many cases he was cut off as other men are by premature death; hence there was priest after priest of the order of Aaron to go within the veil for the people. Our Lord Jesus is not as Aaron, who had to be stripped of his garments on the top of Mount Hor, and to die in the mount; neither is He like to any of the sons of Aaron who in due time suffered the infirmities of age, and at last bowed their heads to inevitable death. He died once, but death has no more dominion over Him; it is witnessed of Him that He lives.
Amplified: But He holds His priesthood unchangeably, because He lives on forever. (Amplified Bible - Lockman)
KJV: But this man, because he continueth ever, hath an unchangeable priesthood.
NLT: But Jesus remains a priest forever; his priesthood will never end. (NLT - Tyndale House)
Wuest: But this (priest), because He abides forever, has the priesthood which is non-transferable,
Young's Literal: and he, because of his remaining--to the age, hath the priesthood not transient,
BUT JESUS, ON THE OTHER HAND BECAUSE HE CONTINUES FOREVER HOLDS HIS PRIESTHOOD PERMANENTLY: ho de dia to menein (PAN) auton eis ton aiona echei (3SPAI) ten hierosunen: (Heb 7:8-25,28; 13:8; Isaiah 9:6,7; John 12:34; Romans 6:9; Revelation 1:18 ) (1 Samuel 2:35)
Spurgeon on Jesus...continues forever - Here is our comfort: We have only one priest, and He ever lives. He had no predecessor and He will have no successor, because He ever lives personally to exercise the office of high priest on our behalf. My soul reposes in the faith of His one sacrifice, offered once and no more. There is but one presenter of that one sacrifice, and never can there be another, since the One is all-sufficient, and He never dies. Jesus reads my heart, and has always read it since it began to beat: He knows my griefs and has carried my sorrows from of old, and He will bear both them and me when old age shall shrivel up my strength. When I myself shall fall asleep in death He will not die, but will be ready to receive me into His own undying blessedness.
Permanently (531) (aparabatos) from a = w/o + parabaíno = go beyond, transgress) is literally that which does not go beyond and thus does not pass away. It means more than incidental permanence or something that simply will not be changed. It means unchangeable, unalterable, inviolable. It is something that cannot be changed. Carries idea of “valid and unalterable” and in secular Greek was used at the end of legal contracts.
Wuest notes that aparabatos "describes that which cannot be violated, or that which does not pass over to another. The priestly ministry of Messiah is in view here, a ministry such that no other person can step into it, a ministry that cannot be transferred to another." (Hebrews Commentary online)
Jesus’ priesthood does not just happen to be permanent. It cannot possibly be anything but permanent. It is not capable of anything but permanence. By its very divine nature it can never conclude or weaken or become ineffective. Jesus Christ has a priesthood that is absolutely incapable of ever being altered in any way! He is the last High Priest. No other will ever be needed.
Spurgeon - I think they reckoned that there were eighty-three high priests in regular succession from Aaron to the death of Phineas, the last high priest at the siege of Jerusalem. One succeeded another, but this one goes on continually, forever has an untransferable priesthood. We know no priests on earth now, save that in a secondary sense the Lord Jesus has made all believers to be kings and priests unto God. We have now no special order of persons set apart to represent their fellows before God. Under the Mosaic dispensation there were many priests not suffered to continue by reason of death; but under the Christian dispensation we have only one priest, who continues ever in an untransferable priesthood.