The Cloud of Unknowing (14th Century)

The Cloud of Unknowing is a practical spiritual guidebook thought to have been written in the 14th century by an anonymous English monk who counsels a young student to seek God not through knowledge but through love. "Our intense need to understand will always be a powerful stumbling block to our attempts to reach God in simple love [...] and must always be overcome", he writes. "For if you do not overcome this need to understand, it will undermine your quest. It will replace the darkness which you have pierced to reach God with clear images of something which, however good, however beautiful, however Godlike, is not God."

The book, which draws on the mystical tradition of Pseudo-Dionysius the Areopagite, has reputedly inspired generations of mystical searchers from St. John of the Cross to Teilhard de Chardin. 

From Wikipedia  

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