Know that God Most High has a mystery in the human heart. It is hidden in it just as fire in iron; when a stone is struck on iron the mystery (fire) is made manifest and plain. In the same way listening to fine music (sama-i khush) and rhythmic song (awaz-i mawzun) excites that essence in the heart. Something appears in it without a person's having any choice about it. The reason for this is the relationship that the essence of every human being has with the World of the Sublime: that which is called the world of spirits. The Sublime World is the world of excellence and beauty; the basis of excellence and beauty is proportion; whatever is in proportion gives proof of the beauty of that world. For, every beauty, excellence, and proportionality that is perceived in this world is all the fruit of the beauty, excellence and proportionality of that world.
Therefore, a sweet, rhythmic, proportioned song also has a resemblance to the marvels of that world. Because of this, an awareness is awakened in the heart. A movement, a yearning or longing is born that the (listener) himself may not understand what it is. This is in a heart which is simple and devoid of being affected by passion and yearning. However, if it is not empty and is occupied with something, that with which it is occupied starts to move and brighten as does a flame when it is breathed upon.
For the person whose heart has been conquered by the fire of the love of God Most High, music is important, for it makes that fire burn hotter. However, for anyone whose heart harbors love for the false, music is fatal poison for him and is forbidden to him. (Alchemy, p 425)
Laleh Bakhtiar, Al-Ghazzali His Psychology of the Greater Struggle
Pic above: Naqshbandi Haqqani ar Rabbani whirling Dervishes from Indonesia