The philosophic mystic seeks to rise from what is sense-tied to what is sense-free, from the appearance of reality to the pure reality itself. The perceptual symbols and optical phenomena which are so often labelled "mystical" are, therefore, a degree less sensuous to him than their physical counterparts. They are helps at first on the upward way, but they become hindrances in the end. To live permanently in the midst of a psychic mirage, however pleasant or dazzling it seems at the time, is not going to help his true advancement in this path. He should be warned by their appearance not to dally too long with them, but to pass them by unheeded and seek the true insight ahead. This rule is pushed to such an extent in the highest mystical circles of Tibet that the lama-student who has emerged from his novitiate is even warned against accepting as the goal the visions of an enveloping universal light--which is the supreme clairvoyant vision possible for man--and told that this is merely a test of his fixed purpose and a trap for his metaphysical knowledge. He is warned that they will pass as they come. They are useful as steps to the Truth, but they are not the permanent realization of truth itself. Those who are babes just emerging from the wood of ignorance may see the mystic light in a temporary clairvoyant vision, but those who are grown adults will know it always as the principle of pure consciousness which makes all vision, whether clairvoyant or physiological, possible. The divine reality being the ultimate and undisclosed basis of all existences, if we externalize it in spectacular visions and phenomenal experiences, we miss its pure being and mix it up with mere appearance. Thus the very experiences which are considered signs of favourable progress in meditation on the mystic's path become signs of hindrance on the philosopher's path.
-- Notebooks Category 20: What Is Philosophy? > Chapter 4: Its Realization Beyond Ecstasy > # 10