“And no man taketh this honour unto himself, but he that is called of God, as was Aaron.”
King James Version (KJV)
5:4 The apostle begins here to treat of the priesthood of Christ. The sum of what he observes concerning it is, Whatever is excellent in the Levitical priesthood is in Christ, and in a more eminent manner; and whatever is wanting in those priests is in him. And no one taketh this honour - The priesthood. To himself, but he that is called of God, as was Aaron - And his posterity, who were all of them called at one and the same time. But it is observable, Aaron did not preach at all; preaching being no part of the priestly office.
Heb 5:4 And no man taketh this honour unto himself. He must be called to it by God. As [was] Aaron. Aaron was so appointed. See Ex 28:1 Le 8:2.