10. Prolong thy mercy to them that know thee. David now sets himself to pray. And, first, he asks in general, that God would continue his mercy to all the godly, and then he pleads particularly in his own behalf, imploring the help of God against his enemies. Those who affirm that God is here said to prolong or extend his mercy because it is exalted above the heavens, indulge in a style of speaking too puerile. When David spake of it in such terms in a preceding verse, his intention was not, as I have already said, to represent the mercy of God as shut up in heaven, but simply to declare that it was diffused throughout the world; and here what he desires is just this, that God would continue to manifest, even to the end, his mercy towards his people. With the mercy of God he connects his righteousness, combining them as cause and effect. We have already said in another place, that the righteousness of God is manifested in his undertaking the defense of his own people, vindicating their innocence, avenging their wrongs, restraining their enemies, and in proving himself faithful in the preservation of their welfare and happiness against all who assail them. Now, since all this is done for them freely by God, David, with good reason, makes mention particularly of his goodness, and places it first in order, that we may learn to depend entirely upon his favor. We ought also to observe the epithets by which he describes true believers; first, he says, that they know God; and, secondly, that they are upright in heart. We learn from this that true godliness springs from the knowledge of God, and again, that the light of faith must necessarily dispose us to uprightness of heart. At the same time, we ought always to bear in mind, that we only know God aright when we render to him the honor to which he is entitled; that is, when we place entire confidence in him.