David vs. Paul?

Here is how John Calvin reconciles David's delight in God's law in Psalm 19 and Paul's approbation of  the law in certain parts of his writings.

But in the first place, we must remember what I have shown you at the commencement, that David does not speak simply of the precepts of the Moral Law, but comprehends the whole covenant by which God had adopted the descendants of Abraham to be his peculiar people; and therefore to the Moral Law-the rule of living well- he joins the free promises of salvation, or rather Christ himself, in whom and upon whom this adoption is founded. But Paul who had to deal with persons who perverted and abused the law, and separated it from the grace and Spirit of Christ, refers to the ministry of Moses viewed merely by itself, and according to the letter.

It is  certain, that if the Spirit of Christ does not quicken the law, the law is not only unprofitable, but also deadly to its disciples. Without Christ there is in the law nothing but inexorable rigor, which adjudges all mankind to the wrath and curse of God. And farther, without Christ, there remains within us a rebelliousness of the flesh, which kindles in our hearts a hatred of God and his law, and from this proceed the distressing bondage and awful terror of which the Apostle speaks. 

These different ways in which the law may be viewed, easily show us the manner of reconciling these passages of Paul and David, which seem at  first view to be at variance. The design of Paul it so to show what the law can do for us, taken by itself; that is to say, what it can do for us when, without the promise of grace, it strictly and rigorously exacts from us the duty which we owe to God; but David, in praising it, as he here does, speaks of the whole doctrine of the law, which includes the gospel, and, therefore under the law he comprehends Christ. 

Spurgeon on the Law and Gospel

I especially liked the last sentence. Notice that Spurgeon does not say the law is there simply to drive us to Christ and show us our sin. Of course, Spurgeon believed this. But here he states that the Gospel produces a life that is consistent with God's law.

"There are certain pious moderns who will not allow the preacher to speak upon anything but those doctrinal statements concerning the way of salvation which are known as 'the Gospel.' We do not stand in awe of such criticism, for we clearly perceive that our Lord Jesus Christ himself would very frequently have come under it. Read the Sermon on the Mount and judge whether certain among the pious would be content to hear the like of it preached to them. Indeed, they would condemn it as containing very little Gospel and too much good works. They would condemn it as containing all too much of the legal. But we must never let be forgotten Christ's emphasis: the law must be preached, for what the law demands of us, the Gospel produces in us, else ours is no Gospel at all." Charles Haddon Spurgeon

HT: George Grant