This book is a 16th-century treatise to the poem The Dark Night of The Soul by the Spanish writer John of the Cross. It gives a commentary on the poem and practical advice on the ascetical life, the final aim which is the union with God. Part of the advice is based on the author's experience of the spiritual search. Together with the poem and the other treatise The Dark Night, this work belongs to the most important writings of the Spanish spiritual mysticism.

John of the Cross (1542 - 1591), also known as Saint John of the Cross, was a Spanish Catholic priest, mystic, and a Carmelite friar of converso origin. He was a significant figure of the Counter-Reformation in Spain, one of the thirty-six Doctors of the Church? And also one of the most famous Christian writers of his time. His studies of the development of soul and spirit belong to the most outstanding examples of Spanish literature and are considered masterpieces for their rich imagery and symbolism.