Verse 1-7 — Be merciful unto me, O God. This petition includes all the good for which we come to throne of grace. If we obtain mercy there, we need no more to make us happy. It implies likewise our best plea, not our merit, but God's mercy, his free, rich mercy. We may flee to, and trust the mercy of God, when surrounded on all sides by difficulties and dangers. His enemies were too hard for him, if God did not help him. He resolves to make God's promises the matter of his praises, and so we have reason to make them. As we must not trust an arm of flesh when engaged for us, so we must not be afraid of an arm of flesh when stretched out against us. The sin of sinners will never be their security. Who knows the power of God's anger; how high it can reach, how forcibly it can strike?
Verse 8-13 — The heavy and continued trials through which many of the Lord's people have passed, should teach us to be silent and patient under lighter crosses. Yet we are often tempted to repine and despond under small sorrows. For this we should check ourselves. David comforts himself, in his distress and fear, that God noticed all his grievances and all his griefs. God has a bottle and a book for his people's tears, both the tears for their sins, and those for their afflictions. He observes them with tender concern. Every true believer may boldly say, The Lord is my helper, and then I will not fear what man shall do unto me; for man has no power but what is given him from above. Thy vows are upon me, O Lord; not as a burden, but as that by which I am known to be thy servant; as a bridle that restrains me from what would be hurtful, and directs me in the way of my duty. And vows of thankfulness properly accompany prayers for mercy. If God deliver us from sin, either from doing it, or by his pardoning mercy, he has delivered our souls from death, which is the wages of sin. Where the Lord has begun a good work he will carry it on and perfect it. David hopes that God would keep him even from the appearance of sin. We should aim in all our desires and expectations of deliverance, both from sin and trouble, that we may do the better service to the Lord; that we may serve him without fear. If his grace has delivered our souls from the death of sin, he will bring us to heaven, to walk before him for ever in light.