JFB : Psalms 126

      @Ps 126:1-6. To praise for God's favor to His people is added a prayer for its continued manifestation.

      1-3. When the Lord, &c.--The joy of those returned from Babylon was ecstatic, and elicited the admiration even of the heathen, as illustrating God's great power and goodness.
      turned again the captivity--that is, restored from it (@Job 39:12 Ps 14:7 Pr 12:14). HENGSTENBERG translates: "When the Lord turned Himself to the turning of Zion" (see Margin), God returns to His people when they return to Him (@De 30:2,3).

      4. All did not return at once; hence the prayer for repeated favors.
      as the streams in the south--or, the torrents in the desert south of Judea, dependent on rain (@Jos 15:9), reappearing after dry seasons (compare @Job 6:15 Ps 68:9). The point of comparison is joy at the reappearing of what has been so painfully missed.

      5, 6. As in husbandry the sower may cast his seed in a dry and parched soil with desponding fears, so those shall reap abundant fruit who toil in tears with the prayer of faith. (Compare the history, @Ezr 6:16,22).

      6. He that goeth forth--literally, better, "He goes--he comes, he comes," &c. The repetition implies there is no end of weeping here, as there shall be no end of joy hereafter (@Isa 35:10).
      precious seed--rather, seed to be drawn from the seed box for sowing; literally, "seed-draught." Compare on this Psalm, @Jer 31:9, &c.