This forms a very suitable prayer, after the experience of such unlooked for mercies. The streams in the south most probably refer to those subterraneous waters that empty themselves, and are seen no more. Babylon no more retains her captives. The spiritual Babylon hath a period also, when it shall be known no more. Rev_18:2; Rev_18:20-21.
Related Commentaries of Psalms 126:4
Psalms 126:4
4 Turn again our captivity, O LORD, as the streams in the south.