Hebrews 7:24

But this - Ὁ δε, But he, that is, Christ, because he continueth ever - is eternal, hath an unchangeable priesthood, απαραβατον ἱερωσυνην, a priesthood that passeth not away from him; he lives for ever, and he lives a priest for ever.

But this man - Greek "But he" - referring to Christ.

Because he continueth ever - Greek "Because he remains forever." The idea is because he does not die, but ever lives, he has an unchanging priesthood. There is no necessity that he should yield it to others, as was the case with the Jewish priests because they were mortal. The reason in their case, why it passed to others, was not that they did not perform the office well, but that they were mortal, and could not continue to hold it. But this reason could not operate in the case of the Lord Jesus, and therefore his priesthood would be permanent.

Hath an unchangeable priesthood - Margin, "or, "which passeth not from one to another." The margin expresses the sense of the passage. The idea is not strictly that it was "unchangable," but that "it did not pass over into other hands." The Levitical priesthood passed from one to another as successive generations came on the stage of action. This reasoning is not designed to prove that the priesthood of Christ will be literally "eternal" - for its necessity may cease when all the redeemed are in heaven - but that it is permanent, and does not pass from hand to hand,

7:24 He continueth for ever - In life and in his priesthood. That passeth not away - To any successor.