Charles H. Spurgeon on Psalms 79:9

When the Lord's people are brought very low, let them not look for a lifting up or relief except from God only; therefore say they here, "Help us, O Lord." Such as have laid hold on God for salvation promised in the covenant, may also look for particular deliveries out of particular troubles, as appendices of the main benefit of salvation; therefore, "Help us, O God of our salvation," say they. When men do ask anything, the granting whereof may glorify God, they may confidently expect to have it; and in special when God may be so glorified, and his people may also be preserved and comforted: "Help us (say they) for the glory of thy name: and deliver us." As the conscience of sin useth to step in oftener between us and mercy, so must we call oftener for remission of sin; for earnest affection can double and treble the same petition without babbling; "Deliver us, and purge away our sins." It is the glory of the Lord to forget sin, and when remission of sins is prayed for according to God's promise, the Lord's glory is engaged for the helping of faith to obtain it: "Purge away our sins, for thy name's sake."—David Dickson.