from a sermon by Pope St Leo the Great
…the Church subsists as an integral whole, just as the Apostle says: We are all one in Christ. No difference in office is so great that anyone can be separated, through lowliness, from the head. In the unity of faith and baptism, therefore, our community is undivided. There is a common dignity, as the apostle Peter says in these words: And you are built up as living stones into spiritual houses, a holy priesthood, offering spiritual sacrifices which are acceptable to God through Jesus Christ. And again: But you are a chosen people, a royal priesthood, a holy nation, a people set apart.
For all, regenerated in Christ, are made kings by the sign of the cross; they are consecrated priests by the oil of the Holy Spirit, so that beyond the special service of our ministry as priests, all spiritual and mature Christians know that they are a royal race and are sharers in the office of the priesthood. For what is more king-like than to find yourself ruler over your body after having surrendered your soul to God? And what is more priestly than to promise the Lord a pure conscience and to offer him in love unblemished victims on the altar of one’s heart?