Photo taken in July 2006, at the Discalced Carmelite monastery in Ladue, Missouri.
Mysticism, broadly speaking, is the understanding or experience of the unseen and underlying unity of all things. Saint John of the Cross’ mystical theology is of union with God, Who is the Source of all things. From his book, Ascent of Mount Carmel:
The reason for which it is necessary for the soul, in order to attain to Divine union with God, to pass through this dark night of mortification of the desires and denial of pleasures in all things, is because all the affections which it has for creatures are pure darkness in the eyes of God, and, when the soul is clothed in these affections, it has no capacity for being enlightened and possessed by the pure and simple light of God, if it first cast them not from it; for light cannot agree with darkness; since, as Saint John says: Tenebroe eam non comprehenderunt. That is: The darkness could not receive the light.
The reason is that two contraries (even as philosophy teaches us) cannot coexist in one person; and that darkness, which is affection set upon the creatures, and light, which is God, are contrary to each other, and have no likeness or accord between one another, even as Saint Paul taught the Corinthians, saying: Quoe conventio luci ad tenebras? That is to say: What communion can there be between light and darkness? Hence it is that the light of Divine union cannot dwell in the soul if these affections first flee not away from it….