St Diadochos of Photiki. "On Spiritual Knowledge and Discrimination. One Hundred Texts". From Philokalia, Vol. 1.
36. Let no one who hears us speak of the perceptive faculty of the intellect imagine that by this we mean that the glory of God appears to man visibly. We do indeed affirm that the soul, when pure, perceives God's grace, tasting it in some ineffable manner; but no invisible reality appears to it in a visible form, since now 'we walk by faith, not by sight', as St Paul says (2 Cor. 5:7). If light or some fiery form should be seen by one pursuing the spiritual way, he should not on any account accept such a vision: it is an obvious deceit of the enemy. Many indeed have had this experience and, in their ignorance, have turned aside from the way of truth. We ourselves know, however, that so long as we dwell in this corruptible body, 'we are absent from the Lord' (2 Cor. 5:6) - that is to say, we know that we cannot see visibly either God Himself or any of His celestial wonders.