Paul says: I appeal to you by the mercy of God to present your bodies as a sacrifice, living and holy. The prophet said the same thing: Sacrifice and offering you did not desire, but you have prepared a body for me. Each of us is called to be both a sacrifice to God and his priest. Do not forfeit what divine authority confers on you. Put on the garment of holiness, gird yourself with the belt of chastity. Let Christ be your helmet, let the cross on your forehead be your unfailing protection. Your breastplate should be the knowledge of God that he himself has given you. Keep burning continually the sweet smelling incense of prayer. Take up the sword of the Spirit. Let your heart be an altar. Then, with full confidence in God, present your body for sacrifice. God desires not death, but faith; God thirsts not for blood, but for self-surrender; God is appeased not by slaughter, but by the offering of your free will.
From a sermon by Saint Peter Chrysologus, bishop, 5th century.