“We do not have a complete and satisfying knowledge of the world. We are reduced to the simple conclusion that everywhere in the world there is life like ourselves and that all life is shrouded in mystery. A true acquaintance with the world consists in being filled with a sense of the mystery of existence and life. This mystery becomes only more mysterious with every advance in scientific research. To be filled with the mystery of life is like that which is called in the language of mysticism the "wise ignorance," an ignorance which is nonetheless knowledge of the essential.”

Kulturphilosophie (1923), Vol. 2 : Civilization and Ethics
Context: Affirmation of the world, which means affirmation of the will-to-live that manifests itself around me, is only possible if I devote myself to other life. From an inner necessity, I exert myself in producing values and practising ethics in the world and on the world even though I do not understand the meaning of the world. For in world- and life-affirmation and in ethics I carry out the will of the universal will-to-live which reveals itself in me. I live my life in God, in the mysterious divine personality which I do not know as such in the world, but only experience as mysterious Will within myself.
Rational thinking which is free from assumptions ends therefore in mysticism. To relate oneself in the spirit of reverence for life to the multiform manifestations of the will-to-live which together constitute the world is ethical mysticism. All profound world-view is mysticism, the essence of which is just this: that out of my unsophisticated and naïve existence in the world there comes, as a result of thought about self and the world, spiritual self-devotion to the mysterious infinite Will which is continuously manifested in the universe.

The Power of Myth (1988)

Source: The Witches of Worm

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 422.

" The Life and Teachings of Thoth Hermes Trismegistus http://magdelene.net/Thoth%20Hermes%20Trismegistus.htm", in The Secret Teachings of All Ages (1928) by the Canadian occultist Manly Hall; a few quotation websites credit this to Addison.
Misattributed

Bright Galaxies, Dark Matters (1997), preface

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 91.