It means to utter the sorrow of one’s heart in tears to God.1 It denotes a genuine and an uninhibited plea to God and not a formal religious exercise (see Psalm 62:8). Like water all the sorrows of one’s heart, including all emotion, thoughts and desires are brought before God.2
More light is shed on this verb, pour out,
when taking its other uses in the book of Lamentation into account. In Lamentations 2:4, Lamentations 2:11, and Lamentations 2:12 it is applied to describe how God has poured out or cast down his fury. In Lamentations 2:11–12 it is used to describe the writer’s inward parts that have been cast down or poured out, as well the infants’ lives that are poured out on their mothers’ breasts. If one’s life is poured out, the intercession must match the need by pouring out one’s heart before God, who is not only the author of the calamities, but the only one who can alleviate the need.3
19 Lève-toi, pousse des gémissements à l'entrée des veilles de la nuit! Répands ton cœur comme de l'eau, en présence du Seigneur! Lève tes mains vers lui pour la vie de tes enfants Qui meurent de faim aux coins de toutes les rues!