It is possible either to sustain and strengthen this burning of the spirit, or to quench it. It is warmed above all by acts of love toward God and our neighbor—this, indeed, is the essence of the spiritual life—by the general fidelity to all God’s commandments, with a quiet conscience, by deeds that are pitiless to our own soul and body, and by prayer and thoughts of God. The spirit is quenched by distraction of the attention from God and God’s works, by excessive anxiety about worldly matters, by indulgence in sensual pleasure, by pandering to carnal desires, and by infatuation with material things. If this spirit is quenched, then the Christ life will be quenched too.
—The Art of Prayer