Here we have, I. David's good prayers, by which he sought to God for mercy; these he mentions here, not as boasting of them, or trusting to any merit in them, but reflecting upon them with comfort, that he had taken the appointed way to comfort. Observe here, 1. That he was inward with God in prayer; he prayed with his heart, and prayer is acceptable no further than the heart goes along with it. Lip-labour, if that be all, is lost labour. 2. He was importunate with God in prayer; he cried, as one in earnest, with fervour of affection and a holy vehemence and vigour of desire. He cried with his whole heart; all the powers of his soul were not only engaged and employed, but exerted to the utmost, in his prayers. Then we are likely to speed when we thus strive and wrestle in prayer. 3. That he directed his prayer to God: I cried unto thee. Whither should the child go but to his father when any thing ails him? 4. That the great thing he prayed for was salvation: Save me. A short prayer (for we mistake if we think we shall be heard for our much speaking), but a comprehensive prayer: "Not only rescue me from ruin, but make me happy." We need desire no more than God's salvation (Psa 50:23) and the things that accompany it, Heb 6:9. 5. That he was earnest for an answer; and not only looked up in his prayers, but looked up after them, to see what became of them (Psa 5:3): "Lord, hear me, and let me know that thou hearest me."
II. David's good purposes, by which he bound himself to duty when he was in the pursuit of mercy. "I will keep thy statutes; I am resolved that by thy grace I will;" for, if we turn away our ear from hearing the law, we cannot expect an answer of peace to our prayers, Pro 28:9. This purpose is used as a humble plea (Psa 119:146): "Save me from my sins, my corruptions, my temptations, all the hindrances that lie in my way, that I may keep thy testimonies." We must cry for salvation, not that we may have the ease and comfort of it, but that we may have an opportunity of serving God the more cheerfully.

Hear my voice according unto thy lovingkindness,.... Not according to his own merits and deserts, or works of righteousness done by him, for the sake of which he did not present his supplications to God; nor according to his love to him, which often waxed cold, and he in a poor lukewarm frame of spirit; but according to the lovingkindness of God, which is always the same, and which is a great encouragement to faith and hope in prayer; that since God is gracious and merciful, kind and bountiful, plenteous in mercy, and ready to forgive, on a throne of grace, and full of love, yea, love itself, invariably the same, he will hear, and saints shall find grace and mercy to help them in time of need;

O Lord, quicken me according to thy judgment; either according to his word of promise, or according to his manner and wonted method he used towards his people; see Psa 119:25; This is a prayer, not for the first work of quickening grace, or the first implantation of a principle of spiritual life, which the psalmist had had an experience of; but for the reviving of the work and principle in him, that he might be refreshed and comforted, and be animated and stirred up to a lively exercise of grace and performance of duty: finding himself in dead and lifeless frames, and not able to quicken himself.