Jehovah will recompense upon me, etc. The doubtfulness which attaches to the meaning of the verb gmr, gamar, throws an uncertainty over the whole sentence. Sometimes it signifies to repay, and, in general, to bestow, for it is often applied to free favors. Yet the context would seem to require.another sense, since, when it is added as a reason, that Jehovah's mercy is everlasting, and that he will not forsake the works of his hands, the better sense would seem to be -- Jehovah will perform for me, that is, will continue to show that he cares for my safety, and will fully perfect what he has begun. Having once been delivered by an act of Divine mercy, he concludes that what had been done would be perfected, as God's nature is unchangeable, and he cannot divest himself of that goodness which belongs to him. There can be no doubt that the way to maintain good hope in danger is to fix our eyes upon the Divine goodness, on which our deliverance rests. God is under no obligation on his part, but when, of his mere good pleasure, he promises to interest himself in our behalf. David concludes with the best reason, from the eternity of the Divine goodness, that the salvation granted him would be of no limited and merely evanescent character. This he confirms still farther by what he adds, that it is impossible God should leave his work, as men may do, in an imperfect or unfinished state through lassitude or disgust. This David is to be understood as asserting in the same sense in which Paul declares, that "the gifts and calling of God are without repentance." (Romans 11:29.) Men may leave off a work for very slight reasons which they foolishly undertook from the first, and from which they may have been diverted through their inconstancy, or they may be forced to give up through inability what they enterprised above their strength; but nothing of this kind can happen with God, and, therefore, we have no occasion to apprehend that our hopes will be disappointed in their course towards fulfillment. Nothing but sin and ingratitude on our part interrupts the continued and unvarying tenor of the Divine goodness. What we firmly apprehend by our faith God will never take from us, or allow to pass out of our hands. When he declares that God perfects the salvation of his people, David would not encourage sloth, but strengthen his faith and quicken himself to the exercise of prayer. What is the cause of that anxiety and fear which are felt by the godly, but the consciousness of their own weakness and entire dependence upon God? At the same time they rely with full certainty upon the grace of God, "being confident," as Paul writes to the Philippians, "that he who has begun the good work will perform it till the day of Christ Jesus." (Philippians 1:6.) The use to be made of the doctrine is, to remember, when we fall or are disposed to waver in our minds, that since God has wrought the beginning of our salvation in us, he will carry it forward to its termination. Accordingly, we should betake ourselves to prayer, that we may not, through our own indolence, bar our access to that continuous stream of the divine goodness which flows from a fountain that is inexhaustible.

The Lord will perfect that which concerneth me - He will complete what he has begun. He will not begin to interpose in my behalf, and then abandon me. He will not promise to save me, and then fail to fulfill his promise. He will not encourage me, and then cast me off. So of us. He will complete what he begins. He will not convert a soul, and then leave it to perish. "Grace will complete what grace begins." See the notes at Philippians 1:6.
Thy mercy, O Lord, endureth for ever - See the notes at Psalm 136:1.
Forsake not the works of thine own hands - What thou hast made; what thou hast begun to do. Do not leave me to perish. Prayer is one of the means - and an essential means - by which the saints are to be kept unto salvation. The doctrine of the "perseverance of the saints." is not inconsistent with prayer, but rather prompts to it; and he who professes to rely on that doctrine, and feels so safe that he does not need to pray, and does not pray, gives certain evidence that he has never been converted, and has no true religion.

The Lord will perfect - Whatever is farther necessary to be done, he will do it.
Forsake not the works of thine own hands - My body - my soul; thy work begun in my soul; thy work in behalf of Israel; thy work in the evangelization of the world; thy work in the salvation of mankind. Thou wilt not forsake these.

The LORD will (f) perfect [that which] concerneth me: thy mercy, O LORD, [endureth] for ever: forsake not the works of thine own hands.
(f) Though my enemies rage, yet the Lord, who has begun his work in me, will continue his grace to the end.

The Lord will perfect that which concerneth me,.... Or "will", or "may the Lord perform for me" (x): all things in providence; all that he had appointed for him, that would be for his good and his own glory, Psalm 57:2; and particularly what concerned him as a king. He had made him king over the house of Judah; he had begun to fulfil his promise concerning the kingdom; and he would perfect it, by setting him over all the tribes of Israel. Also he believed he would perfect what concerned him as a saint, even the good work of grace upon his heart; which is but a begun work, is imperfect, is gradually carried on, and will be completed; God is able to do it, and none can hinder him; he has promised to do it, and he is faithful who will do it; and his glory is concerned in it; and it may be depended on it will be finished; he is a rock, and his work is perfect; see Philippians 1:6;
thy mercy, O Lord, endureth for ever; a phrase often used by the psalmist, with which his heart was affected; and here used, both as an argument by which he concluded God would perfect his begun work, and as an encouragement to make the following request:
forsake not the works of thine own hands; as are all the works of providence and grace: the work of grace upon the heart may be expressed in the plural number, because of the several branches of it; which are all so many works, as the work of faith, labour, of love, &c. 1-Thessalonians 1:3; and which is the Lord's handiwork; and a curious work it is, a new creation work, a work of almighty power; and which he will never cease from, or be remiss in, as the word (y) signifies, until he has accomplished it, 2-Thessalonians 1:11. It is a prayer of faith, and may be most confidently believed: and some indeed render it as an expression of faith, "thou wilt not forsake the works of thine hands" (z); David himself was the work of God's hands, as Kimchi observes, as a creature, as a king, and as a saint; and so are all the people of God, Isaiah 45:11; and whom he will never leave nor forsake; for they are his church, his chosen, his children, his portion and inheritance, Psalm 94:14.
(x) "perficiet pro me", Montanus, Musculus; "perficiat pro me", Junius & Tremellius. (y) "ne dimittas", Pagninus, Montanus. (z) "Non deseres", Musculus, Piscator.

God will fulfil His promise.

Perfect - Will finish the great work of my deliverance. Forsake not - Or, do not give over, the work of my salvation, which is thus far advanced, not by any human help, but by thy power and providence.