|Thanks Wiki for the photo http://en.wikipedia.org/wiki/Knights_Hospitaller|
Since this is the proper moment, we ought to point out another benefit resulting from this night and dryness of the sensory appetite. So that the prophecy -- your light will illumine the darkness [Is. 58:10] -- may be verified, God will give illumination by bestowing on the soul not only knowledge of its own misery and lowliness but also knowledge of his grandeur and majesty. When the sensory appetites, gratifications, and supports are quenched, the intellect is left clean and free to understand the truth, for even though these appetites and pleasures concern spiritual things, they blind and impede the spirit. Similarly, the anguish and dryness of the senses illumine and quicken the intellect, as Isaiah affirms: Vexation makes one understand [Is. 28:19]. But God also, by means of this dark and dry night of contemplation, supernaturally instructs in his divine wisdom the soul that is empty and unhindered (which is the requirement for his divine inpouring), which he did not do through the former satisfactions and pleasures.
On the senses being purified....from St. John of the Cross