In these verses we may observe,
I. With what pleasure David looks back upon what God had done for him formerly (v. 5): Thou, O God! hast heard my vows, that is, 1. "The vows themselves which I made, and with which I bound my soul: thou hast taken notice of them; thou hast accepted them, because made in sincerity, and been well pleased with them; thou hast been mindful of them, and put me in mind of them." God put Jacob in mind of his vows, Gen. xxxi. 13; xxxv. 1. Note, God is a witness to all our vows, all our good purposes, and all our solemn promises of new obedience. He keeps an account of them, which should be a good reason with us, as it was with David here, why we should perform our vows, v. 8. For he that hears the vows we made will make us hear respecting them if they be not made good. 2. "The prayers that went along with those vows; those thou hast graciously heard and answered," which encouraged him now to pray, O God! hear my cry. He that never did say to the seed of Jacob, Seek you me in vain, will not now begin to say so. "Thou hast heard my vows, and given a real answer to them; for thou hast given me a heritage of those that fear thy name." Note, (1.) There is a peculiar people in the world that fear God name, that with a holy awe and reverence accept of and accommodate themselves to all the discoveries he is pleased to make of himself to the children of men. (2.) There is a heritage peculiar to that peculiar people, present comforts, earnests of their future bliss. God himself is their inheritance, their portion for ever. The Levites that had God for their inheritance must take up with him, and not expect a lot like their brethren; so those that fear God have enough in him, and therefore must not complain if they have but little of the world. (3.) We need desire no better heritage than that of those who fear God. If God deal with us as he uses to deal with those that love his name we need not desire to be any better dealt with.
II. With what assurance he looks forward to the continuance of his life (v. 6): Thou shalt prolong the king's life. This may be understood either, 1. Of himself. If it was penned before he came to the crown, yet, being anointed by Samuel, and knowing what God had spoken in his holiness, he could in faith call himself the king, though now persecuted as an out-law; or perhaps it was penned when Absalom sought to dethrone him, and force him into exile. There were those that aimed to shorten his life, but he trusted to God to prolong his life, which he did to the age of man set by Moses (namely, seventy years), which, being spent in serving his generation according to the will of God (Acts xiii. 36), might be reckoned as many generations, because many generations would be the better for him. His resolution was to abide in God's tabernacle for ever (v. 4), in a way of duty; and now his hope is that he shall abide before God for ever, in a way of comfort. Those abide to good purpose in this world that abide before God, that serve him and walk in his fear; and those that do so shall abide before him for ever. He speaks of himself in the third person, because the psalm was delivered to the chief musician for the use of the church, and he would have the people, in singing it, to be encouraged with an assurance that, notwithstanding the malice of his enemies, their king, as they wished, should live for ever. Or, 2. Of the Messiah, the King of whom he was a type. It was a comfort to David to think, whatever became of him, that the years of the Lord's Anointed would be as many generations, and that of the increase of his government and peace there should be no end. The Mediator shall abide before God for ever, for he always appears in the presence of God for us, and ever lives, making intercession; and, because he lives, we shall live also.
III. With what importunity he begs of God to take him and keep him always under his protection: O prepare mercy and truth which may preserve him! God's promises and our faith in them are not to supersede, but to quicken and encourage prayer. David is sure that God will prolong his life, and therefore prays that he would preserve it, not that he would prepare him a strong lifeguard, or a well-fortified castle, but that he would prepare mercy and truth for his preservation; that is, that God's goodness would provide for his safety according to the promise. We need not desire to be better secured than under the protection of God's mercy and truth. This may be applied to the Messiah: "Let him be sent in the fulness of time, in performance of the truth to Jacob and the mercy to Abraham." Micah vii. 20; Luke i. 72, 73.
IV. With what cheerfulness he vows the grateful returns of duty to God (v. 8): So will I sing praise unto thy name for ever. Note, God's preservation of us calls upon us to praise him; and therefore we should desire to live, that we may praise him: Let my soul live, and it shall praise thee. We must make praising God the work of our time, even to the last (as long as our lives are prolonged we must continue praising God), and then it shall be made the work of our eternity, and we shall be praising him for ever. That I may daily perform my vows. His praising God was itself the performance of his vows, and it disposed his heart to the performance of his vows in other instances. Note, 1. The vows we have made we must conscientiously perform. 2. Praising God and paying our vows to him must be our constant daily work; every day we must be doing something towards it, because it is all but little in comparison with what is due, because we daily receive fresh mercies, and because, if we think much to do it daily, we cannot expect to be doing it eternally.