The Dark Night of the Soul (Spanish: La noche oscura del alma) is a phase of passive purification in the mystical development of the individual's spirit, according to the 16th-century Spanish mystic and Catholic poet St. John of the Cross. John describes the concept in his treatise Dark Night (Noche Oscura), a commentary on his poem with the same name. It follows after the second phase, the illumination in which God's presence is felt, but this presence is not yet stable. The author himself did not give any title to his poem, which together with this commentary and the Ascent of Mount Carmel (Subida del Monte Carmelo) forms a treatise on the active and passive purification of the senses and the spirit, leading to mystical union. In modern times, the phrase "dark night of the soul" has become a popular phrase to describe a crisis of faith or a difficult, painful period in one's life. Source: Wikipedia (en)