Of all spiritual practices: meditation on the sayings of the Prophet and on the traditions of Sufism, meditated recitation of the Qoran, ritual Prayer, and so forth, the dhikr (zekr) is the practice most apt to free spiritual energy, that is, to allow the particle of divine light which is in the mystic to rejoin its like.
The advantage of the dhikr is that it is not restricted to any ritual hour; its only limitation is the personal capacity of the mystic. It is impossible to study the question of colored aphorisms without knowing the spiritual exercise which is their source. Everything takes place, needless to say, in the ghayba, the suprasensory world; what is in question here is solely the physiology of the man of light. Najm Kobra set himself the task of describing the cases and circumstances in which the fire of the dhikr itself becomes the object of mystical apperception. As opposed to the fire of the Devil, which is a dark fire, the vision of which is accompanied by distress and a feeling of overwhelming oppression, the fire of the dhikr is visualized as a pure and ardent blaze, animated by a rapid upward movement. On seeing it, the mystic experiences a feeling of inner lightness, expansion, and intimate relief. This fire enters into the dwelling place like a sovereign prince, announcing: "I alone, and none other than." It sets fire to all that is there to be consumed, and sheds light on any darkness it may encounter. If light is there already, the two lights associate with each other and there is light upon light.
That is why one form of the dhikr above all other, leading in actuality to the acquisition of this pure and ardent flame, consists in repeating the first part of the shahada, the profession of faith: la ilaha illa'llah (Nullus deus nisi Deus), and meditating upon it according the the rules of Sufism. In Ismaelian Shi'ite gnosis, theosophical dialectic was already practiced with extreme subtlety by alternating the negative and affirmative phases composing the first part of the shahada, in order to open up a path between the two abysses, the ta'til and the tashbih, that is to say, between rationalist agnosticism and the literal realism of naive faith. By following this way, the idea of mediating theophanies is established, the hierarchy of the pleroma of light. While the transcendence of the Principle beyond being and non-being is preserved in Ismaelian gnosis, orthodoxy is blamed inasmuch as it falls into the most pernicious kind of metaphysical idolatry, the very one it was so anxious to avoid.
In the Sufism of Najm Kobra, the reiteration of the negative part of the shahada (nullus Deus) is designed to be a weapon against all the powers of the nafs ammara (the lower ego); it consists in denying and rejecting all pretensions to divine prerogatives, all claims inspired in the soul by the instincts of possessiveness and domination. In the positive part of the shahada (nisi Deus) on the other hand the exclusive nature and powers of the One and Only One are affirmed.
Then there comes about the state alluded to in a saying tirelessly repeated by the Sufis, and familiar to us because we have read it in St. Paul (1 Cor. 2 : 9), where in fact it harks back to the Revelation of Elijah. The mystic "sees what the eye has not seen, hears what no ear has heard, while thoughts arise in his mind which had never arisen i n the heart of man," that is to say, of man who remains buried in the depths of natural existence.
For the effect of the fire-light of the dhikr is to make a man clairvoyant in Darkness; and this clairvoyance foretells that the heart is being freed, is emerging from the well of nature; but (let us remember the Sohravardian Recital of the Exile) "only a heart that holds fast to the cable of the Qoran and to the train of the robe of the dhikr escapes from the well of nature."
From: The Man of Light in Iranian Sufism