Psalms 126 — Jamieson–Fausset–Brown
126:1–3
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; Psa 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).
126:4
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; Psa 68:9). The point of comparison is joy at the reappearing of what has been so painfully missed.
126:5–6
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).