Psalms 51:12

“Restore unto me the joy of thy salvation, etc.] Not temporal, but spiritual and eternal; and designs either Christ himself, who is God’s salvation, of his appointing and providing, in the view of whom, as such, David had much spiritual joy; or the salvation he was to work out, which God the Father had contrived the scheme of in him, had covenanted with him to do, and had appointed his people to: salvation itself is a sure thing, and can never fail, being founded upon the purpose and counsel of God, which shall ever stand; and is secured in the covenant of grace, which can never be removed; and is now completely wrought out by Christ, and is applied by his Spirit to the heirs of it, who shall…”

“free spirit--"thy" ought not to be supplied, for the word "free" is, literally, "willing," and "spirit" is that of David. "Let a willing spirit uphold me," that is, with a soul willingly conformed to God's law, he would be preserved in a right course of conduct.”

“Restore unto me the joy of thy salvation - literally, “Cause the joy of thy salvation to return.” This implies that he had formerly known what was the happiness of being a friend of God, and of having a hope of salvation. That joy had been taken from him by his sin. He had lost his peace of mind. His soul was sad and cheerless. Sin always produces this effect. The only way to enjoy religion is to do that which is right; the only way to secure the favor of God is to obey his commands; the only way in which we can have comforting evidence that we are his children is by doing that which shall be pleasing to him: 1 John 2:29; 1Jo 3:7, 1 John 3:10. The path of sin is a dark path, and in that path…”

“The joy - The comfortable sense of thy saving grace, promised and vouchsafed to me, both for my present and everlasting salvation. Free - Or, ingenuous, or liberal, or princely. Which he seems to oppose to his own base and illiberal and disingenuous and servile spirit, which he had discovered in his wicked practices: a spirit, which may free me from the bondage of sin, and enable me chearfully to run the way of God's precepts. Psalms 51:14”

“Restore: Psa 85:6-8; Job 29:2, Job 29:3; Isa 57:17, Isa 57:18; Jer 31:9-14 joy: Psa 13:5, Psa 21:1, Psa 35:9; Isa 49:13, Isa 61:10; Luk 1:47; Rom 5:2-11 uphold: Psa 17:5, Psa 19:13, Psa 119:116, Psa 119:117, Psa 119:133; Isa 41:10; Jer 10:23; Rom 14:4; Pe1 1:5; Jde 1:24 free: Rom 8:15; Co2 3:17; Gal 4:6, Gal 4:7 Psalms 51:13”

“In connection with רוּח נדיבה, the old expositors thought of נדיב, a noble, a prince, and נדיבה, nobility, high rank, Job 30:15, lxx πνεύματι ἡγεμονικῷ (spiritu principali) στήριξόν με, - the word has, however, without any doubt, its ethical sense in this passage, Isa 32:8, cf. נדבה, Ps. 54:8; and the relation of the two words רוח נדיבה is not to be taken as adjectival, but genitival, since the poet has just used רוח in the same personal sense in Psa 51:12. Nor are they to be taken as a nominative of the subject, but - what corresponds more closely to the connection of the prayer - according to Gen 27:37, as a second accusative of the object: with a spirit of willingness, of willing,…”