And thus at this time the soul also suffers great darkness in the understanding, many aridities and afflictions in the will, and grievous knowledge of its miseries in the memory, for the eye of its spiritual self-knowledge is very bright. And in its substance the soul suffers profoundly from its poverty and abandonment.
Now, since this is the remedy and medicine that God gives to the soul for its many infirmities, that he may bring it health, the soul must needs suffer in the purgation and remedy, according to the nature of its sickness. For here its heart is laid upon the coals, so that every kind of evil spirit is driven away from it; and here its infirmities are continually brought to light and are laid bare before its eyes that it may feel them, and then they are cured. And that which aforetime was hidden and set deep within the soul is now seen and felt by it, in the light and heat of the fire, whereas aforetime it saw nothing. Even so, in the water and smoke that the fire drives out of wood are seen the humidity and the frigidity that it had aforetime, though this was realized by none. But now, being brought near to this flame, the soul clearly sees and feels its miseries, for - oh, wonderful thing! - there arise within it contraries against contraries against contraries, some of which, as the philosophers say, bring the others to light; and they make war in the soul, striving to expel each other in order that they may reign within it.
God, who is all perfection, wars against all the imperfect habits of the soul, and, purifying the soul with the heat of his flame, he uproots its habits from it, and prepares it, so that at last he may enter it and be united with it by his sweet, peaceful, and glorious love, as is the fire when it has entered the wood.
(Saint John of the Cross)