16th century Spanish poet, Roman Catholic mystic and Carmelite priest, Saint John of the Cross, wrote the poem Dark Night of the Soul and latera treatise commenting on the poem. It was written while John of the Cross was imprisoned by his Carmelite brothers, in opposition to his reformation of their Order, and narrates the journey of the soul from its bodily home to its union with God. The night in which the journey takes place represents the hardships and problems the soul meets in detaching from the world to achieve union with the Creator, represented by the light.
Successive stanzas relate the steps in this night journey. Central is the painful experience people endure in order to grow in spiritual maturity and union with God.
There are two phases of the dark night: first is a purification of the senses, and second the more intense purification of the spirit. The poem is divided into two books to that cover these phases. Saint Thomas Aquinas, following on from Aristotle’s ideas, described ten steps on the ladder of mystical love. They are further described in Dark Night of the Soul. John of the Cross later wrote the treatise, as a theological commentary on the poem, explaining its meaning stanza by stanza.
You can read more about John of the Cross and other ancient and contemporary mystics in my blog A Reasonable Mystic, in which I discuss the place of mysticism in contemporary and postmodern Christian spirituality.