4 And no one takes this honor on himself, but he receives it when called by God, just as Aaron was.

Read Hebrews 5:4 Using Other Translations

And no man taketh this honour unto himself, but he that is called of God, as was Aaron.
And no one takes this honor for himself, but only when called by God, just as Aaron was.
And no one can become a high priest simply because he wants such an honor. He must be called by God for this work, just as Aaron was.