John Calvin Commentary Hebrews 10:21

"and [having] a great priest over the house of God;" — Hebrews 10:21 (ASV)

And having a high priest, etc. Whatever he has previously said about the abrogation of the ancient priesthood, we ought now to bear in mind, for Christ could not be a priest without the former priests being divested of their office, since it was a different order. He then indicates that all those things which Christ had changed at his coming should be relinquished; and God has set him over his whole house for this purpose—that everyone who seeks a place in the Church should submit to Christ and choose him, and no other, as his leader and ruler.