Hebrews 5:4

4. Taketh… unto himself Who-so, like the sons of Korah or like King Uzziah, assumes the office without divine warrant, is a usurper. The rabbies say that “Moses said to Korah and his associates, ‘If Aaron my brother took the priesthood to himself, you made insurrection against him rightly; but truly God gave it to him.’”

Called of God, as was Aaron Aaron, first in the long line of high priests, was elected by the divine Voice. Exodus 28:1; Exodus 29:4; Leviticus 8:1, etc.; Numbers 3:10, and Numbers 3:16-18. Until the time of Herod the line remained almost unbroken; but by him the office was unlawfully bestowed, and finally ceased just before the destruction of Jerusalem, after continuing through nearly sixteen centuries. Its divine perpetuity was fixed by our great High Priest.