Let us, then, take care not to quench the Spirit. All evil actions extinguish this light: slander, offences and the like. The nature of fire is such that everything foreign to it destroys it, and everything akin to it gives it further strength. This light of the Spirit reacts in the same manner. This is the way in which the spirit of grace manifests itself in Christians. Through repentance and faith it descends into the soul of each [person] in the sacrament of baptism, or else is restored to him [or her] in the sacrament of repentance. The fire of zeal is its essence. But it can take different directions according to the individual.
—The Art of Prayer