“Also, there were many priests, because they were prevented by death from continuing. But He, because He continues forever, has an unchangeable priesthood. Therefore, He is also able to save to the uttermost those who come to God through Him, since He always lives to make intercession for them” (Hebrews 7:23-25).
The first century Jewish historian Josephus estimated that in the 1,400+ years from Mount Sinai to his day, there were 83 men who served as High Priest. (How he arrived at this number is unknown, but it does sound pretty reasonable.) “They were prevented by death from continuing” explains why there were so many.
“But He” explains why the number of New Testament High Priests since Mount Calvary is—and will always remain at—ONE. Because of His immortality (and God’s sworn oath—v. 21), Jesus’ High Priesthood is non-transferable. It is something which exclusively belongs to Him and cannot be given to anyone else.
The wonderful blessing of the permanence of Jesus’ High Priesthood are: He is ever able to save, and He is ever able to save perfectly. Jesus’ ability to save will not in any way diminish over time.
Neither Jesus Himself nor His ability to provide perfect salvation is ever going away. He can save anyone at any time in history. That is God’s permanent offer in the gospel.