From the book The Ascent of Mount Carmel by St. John of the Cross which can be found in text or audio.
The Ascent of Mount Carmel - Book I, The Obscure Night; Chapter I, Two Kinds of this Night
In The Ascent of Mount Carmel, Book I, Chapter I, titled "The Obscure Night," St. John of the Cross discusses two types of spiritual "nights" that the soul experiences on its journey toward union with God. The first is the "night of the senses," where one detaches from worldly pleasures and sensory experiences. The second is the "night of the spirit," a more profound and challenging purification where the soul undergoes spiritual trials, leading to a deeper union with God. This chapter sets the stage for understanding how these dark nights are essential for spiritual growth and the eventual ascent to divine union.