With respect also to spiritual sloth, beginners are apt to be irked by the things that are most spiritual, from which they flee because these things are incompatible with sensible pleasure. For, as they are so much accustomed to sweetness in spiritual things, they are wearied by things in which they find no sweetness. If once they failed to find in prayer the satisfaction which their taste required (and after all it is well that God should take it from them to prove them), they would prefer not to return to it: sometimes they leave it; at other times they continue it unwillingly. And thus because of this sloth they abandon the way of perfection (which is the way of the negation of their will and pleasure for God's sake) for the pleasure and sweetness of their own will, which they aim at satisfying in this way rather than the will of God.And many of these would have God will that which they themselves will, and are fretful at having to will that which He wills, and find it repugnant to accommodate their will to that of God. Hence it happens to them that oftentimes they think that that wherein they find not their own will and pleasure is not the will of God; and that, on the other hand, when they themselves find satisfaction, God is satisfied. Thus they measure God by themselves and not themselves by God, acting quite contrarily to that which He Himself taught in the Gospel, saying: That he who should lose his will for His sake, the same should gain it; and he who should desire to gain it, the same should lose it.
As for the vice of lust - aside from what it means for spiritual persons to fall into this vice, since my intent is to treat of the imperfections that have to be purged by means of the dark night - spiritual persons have numerous imperfections, many of which can be called spiritual lust, not because the lust is spiritual but because it proceeds from spiritual things. It happens frequently that in a person's spiritual exercises themselves, without the person being able to avoid it, impure movements will be experienced in the sensory part of the soul, and even sometimes when the spirit is deep in prayer or when receiving the sacraments of Penance or the Eucharist. These impure feelings arise from any of three causes outside one's control. First, they often proceed from the pleasure human nature finds in spiritual exercises. Since both the spiritual and the sensory part of the soul receive gratification from that refreshment, each part experiences delight according to its own nature and properties. The spirit, the superior part of the soul, experiences renewal and satisfaction in God; and the sense, the lower part, feels sensory gratification and delight because it is ignorant of how to get anything else, and hence takes whatever is nearest, which is the impure sensory satisfaction. It may happen that while a soul is with God in deep spiritual prayer, it will conversely passively experience sensual rebellions, movements, and acts in the senses, not without its own great displeasure. This frequently happens at the time of Communion. Since the soul receives joy and gladness in this act of love - for the Lord grants the grace and gives himself for this reason - the sensory part also takes its share, as we said, according to its mode. Since, after all, these two parts form one individual, each one usually shares according to its mode in what the other receives. As the Philosopher says: Whatever is received, is received according to the mode of the receiver. Because in the initial stages of the spiritual life, and even more advanced ones, the sensory part of the soul is imperfect, God's spirit is frequently received in this sensory part with this same imperfection. Once the sensory part is reformed through the purgation of the dark night, it no longer has these infirmities. Then the spiritual part of the soul, rather than the sensory part, receives God's Spirit, and the soul thus receives everything according to the mode of the Spirit.