I want to provide a little more follow up to my two recent sermons on Psalm 19.
As I pointed out, some view the psalm as having two parts: verses 1-6 on creational revelation, and verses 7-14 on biblical revelation. Others view it as having three sections; the third section is found in verses 12-14, and focuses on heart revelation. On this reading of the psalm, the progression is "nature-scripture-conscience." Of course, the third category is a bit different in that it is subjective rather than objective, and has to do what the ways God’s revelation in creation and Scripture expose the dark places in our hearts. But it is a useful way of looking at the psalm.
As I said in the sermon, we must never separate the book of nature and the book of Scripture from one another. They belong together, they inform one another, they reinforce one another. Jesus calls himself the "bread of life" in biblical revelation (John 6), but obviously knowledge about bread gleaned from natural revelation is necessary for us to fully grasp what Jesus means. David says the law of God is sweeter than honey (Psalm 19), but this metaphorical comparison only works if we have knowledge of honey’s properties through our experience of general revelation.
But, again, as I said in the sermon, the book of Scripture is greater than the book of nature. Natural revelation is just as divine and just as authoritative as biblical revelation, but it is inferior because verbal revelation provides a more complete and direct revelation of God’s redemptive plan.