The following passage is taken from book one, chapter 8, of the Dark Night of the Soul by St. John of the Cross, in which he discusses the night of the senses and the night of the spirit, two kinds of purgations or purifications which occur in the spiritual life. In this particular passage, he speaks briefly of the first night, the purification of the senses, which is experienced by beginners in the spiritual life who are making the transition into the age of proficients, i.e. who are advancing spiritually.
Since the conduct of these beginners in the way of God is lowly and not too distant from love of pleasure and of self, as we explained, God desires to withdraw them from this base manner of loving and lead them on to a higher degree of divine love. And he desires to liberate them from the lowly exercise of the senses and of discursive meditation, by which they go in search of him so inadequately and with so many difficulties, and lead them into the exercise of spirit, in which they become capable of a communion with God that is more abundant and more free of imperfections. God does this after beginners have exercised themselves for a time in the way of virtue and have persevered in meditation and prayer. For it is through the delight and satisfaction they experience in prayer that they have become detached from worldly things and have gained some spiritual strength in God. This strength has helped them somewhat to restrain their appetites for creatures, and through it they will be able to suffer a little oppression and dryness without turning back. Consequently, it is at the time they are going about their spiritual exercises with delight and satisfaction, when in their opinion the sun of divine favor is shining most brightly on them, that God darkens all this light and closes the door and the spring of sweet spiritual water they were tasting as often and as long as they desired. For since they were weak and tender, no door was closed to them, as St. John says in the Book of Revelation [Rv. 3:8]. God now leaves them in such darkness that they do not know which way to turn in their discursive imaginings. They cannot advance a step in meditation, as they used to, now that the interior sense faculties are engulfed in this night. He leaves them in such dryness that they not only fail to receive satisfaction and pleasure from their spiritual exercises and works, as they formerly did, but also find these exercises distasteful and bitter. As I said, when God sees that they have grown a little, he weans them from the sweet breast so that they might be strengthened, lays aside their swaddling bands, and puts them down from his arms that they may grow accustomed to walking by themselves. This change is a surprise to them because everything seems to be functioning in reverse.
This usually happens to recollected beginners sooner than to others since they are freer from occasions of backsliding and more quickly reform their appetites for worldly things. A reform of the appetites is the requirement for entering the happy night of the senses. Not much time ordinarily passes after the initial stages of their spiritual life before beginners start to enter this night of sense. And the majority of them do enter it because it is common to see them suffer these aridities.