Charles H. Spurgeon on Psalms 109:21

But do thou for me, O God the Lord, for thy name's sake. How eagerly he turns from his enemies to his God! He sets the great THOU in opposition to all his adversaries, and you see at once that his heart is at rest. The words are very indistinct and though our version may not precisely translate them, yet it in a remarkable manner hits upon the sense and upon the obscurity which hangs over it. "Do thou for me" —what shall he do? Why, do whatever he thinks fit. He leaves himself in the Lord's hands, dictating nothing, but quite content so long as his God will but undertake for him. His plea is not his own merit, but the name. The saints have always felt this to be their most mighty plea. God himself has performed his grandest deeds of grace for the honour of his name, and his people know that this is the most potent argument with him. What the Lord himself has guarded with sacred jealousy we should reverence with our whole hearts and rely upon without distrust. "Because thy mercy is good, deliver thou me." Not because I am good, but because thy mercy is good: see how the saints fetch their pleadings in prayer from the Lord himself. God's mercy is the star to which the Lord's people turn their eye when they are tossed with tempest and not comforted, for the peculiar bounty and goodness of that mercy have a charm for weary hearts. When man has no mercy we shall still find it in God. When man would devour we may look to God to deliver. His name and his mercy are two firm grounds for hope, and happy are those who know how to rest upon them.