Matthew Poole and continuators on Hebrews 5:4

4 And no man taketh this honour unto himself , but he that is called of God, as was Aaron .

This connecteth the last thing describing the the typical Levitical Priesthood their Call to it. Not any Person whatsoever hath, or can lawfully take to himself the honourable Office of an High Priest, so as to be the Author or End of it. Many have usurped this Office, and others have distributed it contrary to God's Law, whose Priesthood, Offerings, and Ministry are no true ones, especially where Men are self-officiating, corruptly managing of it, as Eli's Sons and Ieroboam's Priests, or self-benefiting by it, 1 Sam. 2.13. &c. and Mich. 3.11. This was so honourable an Office as it was united to the Princedom in Melchisedeck and Jethro.

He that is according to God's Law (the Author of this Priesthood, its Work and Success) qualified in himself, separated from others, and actually honoured by God with it, he ought to take this Office and execute his Work in it to God's Glory, depending on him for his Blessing. Aaron is the particular Instance of the Divine Call to this Office. God separated his Tribe, Family, and Person for his Service in the room of the first-born: God qualified him for it, intailed the High Priesthood to his Seed and Off-spring with the subordinate Priesthood. He solemnly consecrated him by Moses, confirmed him in his Work by Fire from heaven at his first Sacrifice, and vindicates his own Call of him to it by the blossoming Rod, and destroying the Rivals with him for it, Exod. 28.29, 40. Numb. 3.16, 17. and 17.5.

Marginal references: Chro. 26.18.; Exod. 28.1. 1 Chro. 23.13.