This Psalm was composed by Ezra, or some other man of God, at the return of Israel from Babylon.
The church, celebrating and praising God for her return out of the Babylonian captivity, Psa_126:1-3, prayeth him to perfect his work, and foretelleth the good success thereof, Psa_126:4-6.
Turned again the captivity of Zion, i.e. brought the captive Israelites out of Babylon into their own land.
We were like them that dream; we were so surprised and astonished with the report of such a favour, that we could not believe our own eyes and ears, but thought it to be but a dream or delusion of our own fancies; as is usual in matters of great joy, as Gen_45:26Luk_24:11Act_12:9.