Job 30:31

My harp also is turned to mourning, and my organ into the voice of them that weep.

The 'harp' and 'organ' denote the harmonious preaching of Holy Church, whereby in times of peace she sounds forth the joys of the interior life and the praises of the Creator. But when the heat of persecution rises against her, her 'harp is turned to mourning' and her 'organ into the voice of them that weep,' because the sweetness of her preaching is changed into the groaning of lamentation. For in the season of tribulation, Holy Church is not permitted to sound forth the joys she used to tell of, but is compelled to utter forth cries of grief. Her harp sounds to mourning, when instead of speaking of heavenly gladness, she must bemoan present sorrows. Her organ is turned to the voice of weeping, when she who used to sing of future joys now bewails the afflictions she endures. Yet even in this, she does not lose her voice entirely, for her very weeping becomes a kind of music unto God, pleasing in His sight as a sacrifice of a contrite heart.

His adversity partly consisted in the exterior signs of sadness, and so he uses images to show how his signs of joy had been changed. These are either musical instruments, and he expresses this alternative saying, "My lyre was turned to mourning," as if to say: Mourning had taken the place of the lyre I used to use in joy for me; or songs sung by the human voice, and so he says, "and my song," which I used to express my joy, has changed, "to the voice of those who weep."