"... persevere in the work ... For, when you begin it, you will find that there is at the start but a darkness; there is ... a cloud of unknowing. No matter what you do, this darkness and this cloud is between you and your God and because of it you can neither see Him clearly with your reason ... nor can you feel him with you ... love. Be prepared, therefore, to remain in this darkness as long as must be. ... For if you are ever to feel Him or see Him, it will necessarily be within this cloud and within this darkness. ... you are to try to pierce that darkness. ... You are to strike that thick cloud of unknowing with a sharp dart of longing love: and you are not to retreat no matter what comes to pass."
From The Cloud of Unknowing, by an anonymous 14th century English mystic