1. Dark Night of the Soul
His poem narrates the journey of the soul from its bodily home to its union with God. The journey is called "The Dark Night", because darkness represents the hardships and difficulties the soul meets in detachment from the world and reaching the light of the union with the Creator.
There are several steps in this night, which are related in successive stanzas.
The main idea of the poem can be seen as the painful experience that people endure as they seek to grow in spiritual maturity and union with God.
The poem is divided into two books that reflect the two phases of the dark night.
1. The first is a purification of the senses.
2. The second and more intense of the two stages is that of the purification of the spirit, which is the less common of the two.

2. What is the “Dark Night of the Soul?”
The term "dark night (of the soul)" is used in Christianity for a spiritual crisis in a journey towards union with God, like that described by Saint John of the Cross.
Typically for a believer in the dark night of the soul, spiritual disciplines (such as prayer and consistent devotion to God) suddenly seem to lose all their experiential value; traditional prayer is extremely difficult and unrewarding for an extended period of time during this "dark night.“
The individual may feel as though God has suddenly abandoned them or that his or her prayer life has collapsed.
It coincides with the moment in Jesus life when on the Cross he cried out, “Father, Father! Why have You forsaken me?”

3. Rather than resulting in permanent devastation, the dark night is regarded by mystics and others as a blessing in disguise, whereby the individual is stripped (in the dark night of the senses) of the spiritual “high” associated with acts of virtue.
Although individuals may for a time seem to outwardly decline in their practices of virtue, in reality they become more virtuous, as they are being virtuous less for the spiritual rewards (ecstasies in the cases of the first night) obtained and more out of a true love for God.
It is this purgatory, a purgation of the soul, that brings purity and union with God.

5. 3 VIDEOS TO WATCH!
Bishop Barron on dryness in prayer:
Rabbi on “FISH LOVE”
MOTHER THERESA OF CALCUTTA’S DARK NIGHT OF THE SOUL:

6. Some souls who have experienced the “Dark Night”

8. Vocal: http://www.youtube.com/watch?v=-vlcDdwINV0