The reason why the soul not only travels securely when it thus travels in the dark, but makes even greater progress, is this: In general the soul makes greater progress when it least thinks so, yea, most frequently when it imagines that it is losing. Having never before experienced the present novelty which dazzles it, and disturbs its former habits, it considers itself as losing, rather than as gaining ground, when it sees itself lost in a place it once knew, and in which it delighted, traveling by a road it knows not, and in which it has no pleasure.
Asa traveler into strange countries goes by ways strange and untried, relying on information derived from others, and not upon any knowledge of his own—it is clear that he will never reach a new country but by new ways which he knows not, and by abandoning those he knew—so in the same way the soul makes the greater progress when it travels in the dark, not knowing the way.
Butinasmuch as God Himself is here the guide of the soul in its blindness, the soul may well exult and say, “In darkness and in safety,” now that it has come to a knowledge of its state. -St John of the Cross, Dark Night of the Soul