John Calvin on Hebrews 10:21

21. And having a high priest, etc. Whatever he has previously said of the abrogation of the ancient priesthood, it behaves us now to bear in mind, for Christ could not be a priest without having the former priests divested of their office, as it was another order. He then intimates that all those things which Christ had changed at his coming ought to be relinquished; and God has set him over his whole house for this end, — that every one who seeks a place in the Church, may submit to Christ and choose him, and no other, as his leader and ruler. See Appendix L 2.