"melody causes whatever feeling is in the heart to increase"

Whatever is in the heart of man, melody moves and awakens. If a heart full of good feelings and a pure voice are joined together, a great effect is produced. For instance: if there be love in the heart, through melody, it will increase until its intensity can scarcely be borne; but if bad thoughts are in the heart, such as hatred, it will increase and multiply. For instance: the music used in war awakens the desire for bloodshed. The meaning is that melody causes whatever feeling is in the heart to increase. 

- 'Abdu'l-Bahá  (Words to Mrs. Mary L. Lucas, as quoted in "A Brief Account of My Visit to Acca" (Chicago: Bahá'í Publishing Society, 1905), pp. 11-14; The Compilation of Compilations vol. II)