The Dark Night is a commentary on a poem of St. John of the Cross, in which he narrates the journey of the soul to mystical union with God. The darkness represents the unknowable destination which is God, a similar theology to Pseudo-Dionysius the Areopagite. The first verse of the poem is,

In an obscure night
Fevered by love's anxiety
(O hapless, happy plight!)
I went, none seeing me
Forth from my house, where all quiet things are

Here he describes how the body and the mind, are their carnal lusts are made quiet. The "dark night" does not speak of life's trials. Instead the nights which the soul experiences are the purgations on the way to Divine union. The first purgation is that of the sensory part of the soul, the second the spiritual. Such purgations comprise the first of the three stages of the mystical journey, which are followed by illumination and then union.

The work is linked to the Ascent of Mount Carmel which reflects on same principles. They were both written around 1580 but were left unfinished.

St. John was canonized as a saint in 1726 by Pope Benedict XIII and was given the title of doctor of the church.