The Cloud of Unknowing

Evelyn Underhill (6 December 1875 - 15 June 1941) was an English Anglo-Catholic writer and pacifist known for her numerous works on religion and spiritual practice, in particular Christian mysticism.
In the English-speaking world, she was one of the most widely read writers on such matters in the first half of the 20th century. No other book of its type-until the appearance in 1946 of Aldous Huxley's The Perennial Philosophy-met with success to match that of her best-known work, Mysticism, published in 1911.
This book is Evelyn Underhill's translation of the medieval spiritual guidebook called The Cloud of Unknowing, written by an anonymous English monk. At the core is a mystical approach to Christian prayer, in which God is found not through rote knowledge, but through 'blind love.' It has been described as Christianity with a Zen outlook. -J.B. Hare
The Cloud of Unknowing (Middle English: The Cloude of Unknowyng) is an anonymous work of Christian mysticism written in Middle English in the latter half of the 14th century. The text is a spiritual guide on contemplative prayer in the late Middle Ages. The underlying message of this work suggests that the way to know God is to abandon consideration of God's particular activities and attributes, and be courageous enough to surrender one's mind and ego to the realm of "unknowing", at which point one may begin to glimpse the nature of God. (wikipedia.org)