From what has been said, it is clear that God grants the soul in this state the favor of purging it and healing it with this strong lye of bitter purgation, according to its spiritual and its sensual part, of all the imperfect habits and affections which it had within itself with respect to temporal things and to natural, sensual and spiritual things, its inward faculties being darkened, and voided of all these, its spiritual and sensual affections being constrained and dried up, and its natural energies being attenuated and weakened with respect to all this (a condition which it could never attain of itself). In this way God makes it to die to all that is not naturally God, so that, once it is stripped and denuded of its former skin, He may begin to clothe it anew. And thus its youth is renewed like the eagle's and it is clothed with the new man, which, as the Apostle says, is created according to God. This is naught else but His illumination of the understanding with supernatural light, so that it is no more a human understanding but becomes Divine through union with the Divine. In the same way the will is informed with Divine love, so that it is a will that is now no less than Divine, nor does it love otherwise than divinely, for it is made and united in one with the Divine will and love. So, too, it is with the memory; and likewise the affection and desires are all changed and converted divinely, according to God. And thus this soul will now be a soul of heaven, heavenly, and more Divine than human. All this, as we have been saying, and because of what we have said, God continues to do and to work in the soul by means of this night, illumining and enkindling it divinely with yearnings for God alone and for naught else whatsoever.
- St. John of the Cross, Dark Night of the Soul, Book II, Chapter XIII
"This state" is, of course, the dark night of the soul. The Saint's famous work, Dark Night of the Soul, consists of a poem and its drawn-out explication; these two together speak about the night (or, rather, nights--he understands the soul as having two aspects, the sense and the spirit, both of which go through their own dark nights) through which the soul most endure if it is to be purged and conveyed along to the "union of love with God." The dark night comes about as the Lord shines on his people his "supernatural light", which hits our perception as sunlight strikes an owl's, darkening everything. Eventually--and this is one of my favorite images in the whole work--the purging fire in which God refines His people transforms the fuel into a thing like the fire itself: "material fire, acting upon wood, first of all begins to dry it. . . then it begins to make it black. . . and, finally, it begins to kindle it externally and give it heat, and at last transforms it into itself and makes it as beautiful as fire."
This purgation spoken of is actually, according to St. John, one and the same as that which a soul undergoes in Purgatory; for this reason, he explains, the soul which has, in life, reached the highest possible 'step on the ladder to God' will spend no time at all in Purgatory upon death, but will go directly to God.
A friend of mine recently noted that the Catholic concept of Purgatory is roughly analogous to the Protestant idea of sanctification, and in this light Dark Night of the Soul can be read to offer an entirely new meaning (and one admittedly different from the Saint's intended). In this light, the talk of 'human understanding that becomes Divine' may become less frightening to the Protestant reader--it's suddenly more like a Wesleyan idea of "Christian perfection", reached through the Spirit's sanctifying the people of God. Of course, Catholics may read St. John how they will.
I thought that Dark Night of the Soul was a beautiful work. It seems repetitive much of the time, but it's certainly more poetic than those things we deem 'straightforward'; it's also much easier to read than any of the other mystical texts that I've ever picked up. And however you choose to read it, this is, by St. John's own words, a picture of God's work of clothing us with the "new man". There's an idea to relish, to take hope in, and to mold your life around.
Now this I say and testify in the Lord, that you must no longer walk as the Gentiles do, in the futility of their minds. They are darkened in the understanding, alienated from the life of God because of the ignorance that is in them, due to their hardness of heart. They have become callous and have given themselves up to sensuality, greedy to practice every kind of impurity. But this is not the way you learned Christ!--assuming that you have heard about him and were taught in him, as the truth is in Jesus, to put off your old self, which belongs to your former manner of life and is corrupt through deceitful desires, and to be renewed in the spirit of your minds, and to put on the new self, created after the likeness of God in true righteousness and holiness.