The veritable night of the soul begins after the night of the senses, which constitutes its indispensable preparation.
The Dark Night of the Soul, stanza 1:
On a dark night, kindled in love with yearnings—oh, happy chance!—I went forth without being observed, My house being now at rest.
"In the darkness of my understanding and the constraint of my will, in affliction and anguish with respect to memory, remaining in the dark in pure faith, which is dark night for the said natural faculties, the will alone being touched by grief and afflictions and yearnings for the love of God—I went forth from myself; that is, from my low manner of understanding, from my weak mode of loving and from my poor and limited manner of experiencing God, without being hindered therein by sensuality or the devil. This was a great happiness and a good chance for me; for, when the faculties had been perfectly annihilated and calmed, together with the passions, desires and affections of my soul, wherewith I had experienced and tasted God after a lowly manner, I went forth from my own human dealings and operations to the operations and dealings of God. That is to say, my understanding went forth from itself, turning from the human and natural to the Divine; for, when it is united with God by means of this purgation, its understanding no longer comes through its natural light and vigour, but through the Divine Wisdom wherewith it has become united. And my will went forth from itself, becoming Divine; for, being united with Divine love, it no longer loves with its natural strength after a lowly manner, but with strength and purity from the Holy Spirit; and thus the will, which is now near to God, acts not after a human manner, and similarly the memory has become transformed into eternal apprehensions of glory. And finally, by means of this night and purgation of the old man, all the energies and affections of the soul are wholly renewed into a Divine temper and Divine delight."
The friendly presence:
"The spirit must be straitened and inured to hardships as regards its common and natural experience, and be brought by means of this purgative contemplation into great anguish and affliction, and the memory must be borne far from all agreeable and peaceful knowledge, and have an intimated sense and feeling that it is making a pilgrimage and being a stranger to all things, so that it seems to it that all things are strange and of a different kind from that which they were wont to be. For this night is gradually drawing the spirit away from its ordinary and common experience of things and bringing it nearer the Divine sense, which is a stranger and an alien to all human ways. It seems now to the soul that it is going forth from its very self, with much affliction. At other times it wonders if it is under a charm or a spell, and it goes about marvelling at the things that it sees and hears, which seem to it very strange and rare, though they are the same that it was accustomed to experience aforetime. The reason of this is that the soul is now becoming alien and remote from common sense and knowledge of things, in order that, being annihilated in this respect, it may be informed with the Divine—which belongs rather to the next life than to this."
The fruits of the night of the soul:
"Thus it went forth 'without being observed'—that is, without being hindered by these affections, etc., for they were put to sleep and mortified in this night, in the darkness of which they were left, that they might not notice or feel anything after their own low and natural manner, and might thus be unable to hinder the soul from going forth from itself and from the house of its sensuality [...]
Oh, how happy a chance is this for the soul which can free itself from the house of its sensuality! None can understand it, unless, as it seems to me, it be the soul that has experienced it. For such a soul will see clearly how wretched was the servitude in which it lay and to how many miseries it was subject when it was at the mercy of its faculties and desires, and will know how the life of the spirit is true liberty and wealth, bringing with it inestimable blessings."
 Saint John of the Cross, Dark Night of the Soul, Book II, Chapter IV
 Saint John of the Cross, Dark Night of the Soul, Book II Chapter IX
 Saint John of the Cross, Dark Night of the Soul, Book II, chapter XIII