Lev 6:9

“That fire is perpetual that is never extinguished on the altar. The altar of God is our heart. Fire must always burn in it, for the flame of charity must always burn on it for God. Day by day, the priest puts wood on the fire, lest it go out. Everyone who has faith in Christ has been made a member of the high priest. The apostle Peter says to all the faithful, "You are an elect people, a royal priesthood." The apostle John says, "You have made us a kingdom and a priesthood for our God." The priest who feeds the fire on the altar and puts wood on it each day is each one of the faithful. To keep the flame of charity from going out in himself, he does not cease to gather both the examples of the elders and the testimonies of Holy Scripture. To call to mind the examples of the fathers or the precepts of the Lord in the practice of charity is to put fuel on the fire. Since this inner newness of ours grows old in the daily living of life, wood must be used to feed that fire. While the fire grows dim as we age, it grows bright again through the testimonies and examples of the fathers. And the command is good, to gather wood each day in the morning. This cannot be done except when the night of darkness is banished. Since morning is the first part of the day and comes when we have put off thoughts of this present life, each of the faithful should think of this task first so that the practice of charity can inflame whatever is just about to die out in him, by the efforts he can make. For that fire on the altar of God— that is, in our hearts—is soon extinguished unless it is carefully maintained by the examples of the fathers and the testimonies of the Lord. Exposition of the Old and New Testament, Leviticus”

“A holocaust is burned on the altar when a good work is performed with the burning fire of charity in the heart of any elect person who is devoted to God completely (that is, with both body and soul). This is done all night until the morning when one does not cease to persevere in good works throughout all the time of his life, until one is taken from the body and merits seeing the morning of the world to come. The fire will be on the same altar, because we ought to be burning with that charity alone which the Lord gives to his church through the Holy Spirit.”