Note:  Diadochus of Photike does not mean ‘Sing happy music to make the blues go away.’  He means that in melancholy/discouragement, turn to the Pslams, which contain lamentations that look forward in hope.  By joining one’s personal distresses in with the distresses of the Pslams, the hope of the Psalms will become one’s own personal joys.  — PPP