Psalm 51:12

Restore unto me the joy of thy salvation
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 certainly and fully enjoy it; otherwise the glory of all the three Persons in it would be lost: but the joy of it may be interrupted and discontinued for a while, through falls into sin, as this case of David, and the case of Peter, show; and therefore a restoration of it is desired, by showing a fresh interest in this salvation; and particularly by an application of pardoning grace and mercy; see ( Psalms 35:3 Psalms 35:9 ) ( 51:8 ) ;

and uphold me [with thy] free Spirit:
or "let thy free Spirit uphold me" ^F14; the same with the Holy Spirit of God; called "free", because he is a most free and munificent giver: he gives his grace, and bestows his gifts severally, as he pleases, and liberally, and upbraids not; and because he is freely given of God; his graces are freely given, as faith, hope, love and because he frees them to whom he is given from the bondage of sin and corruption, and makes them Christ's free men, and delivers them into the liberty of the children of God; and so is a spirit of adoption, in opposition to a spirit of bondage, by which they have freedom and boldness to call God their Father; and by whom also they have liberty of soul at the throne of grace, and can freely make known their requests, and spread their cases before God; see ( Romans 8:15 Romans 8:16 ) ( 2 Corinthians 3:17 ) ; also he may be so called, because he makes the saints ready and willing to obey the will of God, and to run with cheerfulness the way of his commandments; and is moreover "a princely spirit" ^F15, or beneficent, as some choose to render the words; and which becomes such who are set among princes, and are made kings and priests unto God: and with this spirit the psalmist desires to be "upheld", to be strengthened by it, to do the will and work of God, that so he might not stumble and fall into sin as he had done; that he might be stayed, supported, and comforted with it, as the Holy Spirit of promise; that so he might not faint and sink under his present sense of sin, and the guilt of it; and that he would be not only a guide unto him in the ways of God, but that he would hold up his goings in them, that so he might walk both at liberty and in safety. The Targum interprets this also of the spirit of prophecy.