The Lord rewarded me according to my righteousness
Which, if applied to David, cannot be understood of his own personal righteousness, or of works of righteousness done by him, for these merit nothing at the hand of God; no reward, in strict justice, is due to them, or given to them: a man's own righteousness is imperfect, and by the law of God is not accounted a righteousness; and it is unprofitable to God, is no gain to him, and so not rewardable by him; and were it perfect, it is but man's duty, and what God has a prior right to, and so is not recompensed by him; though it is so far from being pure and perfect, that it is attended with much sin, and is no other than rags, and filthy ones, which can never recommend a person to God; it is what will not bear the sight of God, and can never be called cleanness in his eyesight: by it no man is justified before him; and though God does, indeed, reward the works of his people, which are fruits of his grace, yet the reward is not of debt, but of grace. This, therefore, must be understood of the righteousness of David's cause, and of his innocence with respect to the things he was charged with by his enemies; of his righteousness towards Saul; and of "the cleanness of [his] hands", in not defiling them with his blood, when it was in his power to take away his life; therefore God rewarded him by delivering him out of his hands, and setting him upon the throne, and causing his kingdom to flourish and prosper; for this respects temporal blessings, and not eternal glory and happiness; and is something that had been and was then enjoyed, and not anything future, or in another world: though it is best of all to apply it to Christ, and understand it of his righteousness, which he, as Mediator, has wrought out for his people; this is perfect, pure, and spotless, and entirely agreeable to the law of God; what will bear the sight of God, is satisfying to his justice, is well pleasing to him, and is what he accepts of, and imputes to them that believe in Christ, and by which they are justified from all things. Now, according to this righteousness, Christ in strict justice has been rewarded in his own person; as he had the work of man's redemption assigned him, and he agreed to do it, he had a reward promised him, and which he claimed, when he had glorified his Father and finished his work; and which he received when he was set down at the right hand of God, crowned with glory and honour, in consequence of his obedience, sufferings, and death; see ( Philippians 2:7-10 ) ; and he is rewarded in his members according to his righteousness, they being justified by it, and made heirs of eternal life on account of it, and are or will be glorified with him for evermore;
according to the cleanness of my hands hath he recompensed me;
which signifies the same thing.