The first thing that God gave the created world was physical light. The first communication God makes to the man who has attained His presence is the vision of supernatural Light. This is the doctrine held by the Eastern Church, which calls what is seen "the Uncreated Light." During this rare experience the man feels that he is free from earthly attachments and worldly desires, that the intense peace he enjoys is the true happiness, that God's reality is the overwhelming fact of existence. This vision is a gift, a grace, so it may come suddenly, unexpectedly, but more often it comes to someone who has prepared himself for it by purification and contemplation. It does not last, the Light leaves him as strangely as it came and as independently of his personal control. But its exquisite memory can never leave him. From that date, too, certain beneficial changes appear in his character and his outlook. The lower nature is weakened, the baser attributes are thinned down. From that date, too, certain spiritual truths are confirmed for him, and certain false beliefs are cancelled. Yet, if the vision of Light brought union with God, intimacy with God, it did not and could not enable him to know God as God knows Himself. He could not penetrate His inmost nature and substance. This, the ultimate beyond the Light, is called "the Divine Darkness" by the Fathers of the Eastern Orthodox Church.
-- Notebooks Category 22: Inspiration and the Overself > Chapter 4: Introduction To Mystical Glimpses > # 203