Charles H. Spurgeon on Psalms 126:4

Turn again our captivity, O LORD. A prayer for the perfecting of their deliverance. Let those that are returned to their own land be eased of their burdens which they are yet groaning under. Let those that remain in Babylon have their hearts stirred up, as ours were, to take the benefit of the liberty granted. The beginnings of mercy are encouragements to us to pray for the completing of it. While we are here in this world, there will still be matter for prayer, even when we are most furnished with matter for praise. When we are free, and in prosperity ourselves, we must not be unmindful of our brethren that are in trouble and under restraint. —Matthew Henry.