Quote from : The Merchant of Venice Book

By the sweet power of music: therefore the poet did feign that Orpheus drew trees, stones and floods; since nought so stockish, hard and full of rage, but music for the time doth change his nature. The man that hath no music in himself, nor is not moved with concord of sweet sounds, is fit for treasons, stratagems and spoils; The motions of his spirit are dull as night and his affections dark as Erebus: Let no such man be trusted. Mark the music.