...'the light' already 'shines in the darkness' (Jn. 1:5), both by day and by night, both within and without - within in our hearts (II Cor. 6:16), without in our minds. It shines on us without evening, without change, without alteration, without form. It speaks, works, lives, gives life, and changes into light those whom it illuminates. We bear witness that 'God is light' (I Jn. 1:5) and those to whom it has been granted to see Him have all beheld Him as light, because the light of His glory goes before Him, and it is impossible for Him to appear without light. Those who have not seen His light have not seen Him, for He is the Light, and those who have not received the Light have not yet received grace. Those who have received grace have received the Light of God and have received God, even as Christ Himself, who is the Light, has said, 'I will live in them and move among them' (II Cor. 6:16).
-St. Symeon the New Theologian, Discourses: XXVIII sect. 4, Paulist Press pg. 298, 11th century