One of the main reasons why God calls the Bride into the desert is for detachment. Now, one does not go around in sackcloth and ashes in this stage, but continues doing whatever work God is calling one to do. The cleansing is private, the detachment quiet. In fact, in the Dark Night, one needs more and more solitude in order to hear the very still, small voice of God, as He does not speak to one in thunder or lightening at this stage.
The great gift of the Dark Night is self-knowledge.
Many people fight God instead of entering into the Dark Night of the Soul. This merely delays the stage to purgatory.
4. And here we must note another excellent benefit which there is in this night and aridity of the desire of sense, since we have had occasion to speak of it. It is that, in this dark night of the desire (to the end that the words of the Prophet may be fulfilled, namely: ‘Thy light shall shine in the darkness’84), God will enlighten the soul, giving it knowledge, not only of its lowliness and wretchedness, as we have said, but likewise of the greatness and excellence of God. For, as well as quenching the desires and pleasures and attachments of sense, He cleanses and frees the understanding that it may understand the truth; for pleasure of sense and desire, even though it be for spiritual things, darkens and obstructs the spirit, and furthermore that straitness and aridity of sense enlightens and quickens the understanding, as says Isaias.85 Vexation makes us to understand how the soul that is empty and disencumbered, as is necessary for His Divine influence, is instructed supernaturally by God in His Divine wisdom, through this dark and arid night of contemplation,86 as we have said; and this instruction God gave not in those first sweetnesses and joys.
5. This is very well explained by the same prophet Isaias, where he says: ‘Whom shall God teach His knowledge, and whom shall He make to understand the hearing?’ To those, He says, that are weaned from the milk and drawn away from the breasts.87 Here it is shown that the first milk of spiritual sweetness is no preparation for this Divine influence, neither is there preparation in attachment to the breast of delectable meditations, belonging to the faculties of sense, which gave the soul pleasure; such preparation consists rather in the lack of the one and withdrawal from the other. Inasmuch as, in order to listen to God, the soul needs to stand upright and to be detached, with regard to affection and sense, even as the Prophet says concerning himself, in these words: I will stand upon my watch (this is that detachment of desire) and I will make firm my step (that is, I will not meditate with sense), in order to contemplate (that is, in order to understand that which may come to me from God).88 So we have now arrived at this, that from this arid night there first of all comes self-knowledge, whence, as from a foundation, rises this other knowledge of God. For which cause Saint Augustine said to God: ‘Let me know myself, Lord, and I shall know Thee.’89 For, as the philosophers say, one extreme can be well known by another.