Psalm 19 is a celebration of the resplendent glory of God in both the creation and written word of God. The imagery of light is the key strand that connects the two halves of the psalm. In the first half, in which the psalmist calls us to recognize the greatness of God in the physical universe, the focus is on the sun and the penetrating light of the sun. This picture is then carried through into the second part of the psalm which focuses on God’s word. God’s Word is like the sun in that it gives life but also brings everything into its piercing light. The final prayer of the psalm flows out of this. The psalmist prays that God’s word would indeed give him life by bringing to light the things in him that cause the death of his soul. In this sense he is praying that glory of God, that is reflected in the light of the sun, would shine like the sun in his heart.
When the psalm speaks of the ‘law’ it is not just speaking of lists of rules but of the body of writing that contains God’s covenant with his people. These writings contained not only the laws of and covenant promises of God but also the stories of the patriarchs and of Israel which formed key historical covenant precedents. The law (Torah in Hebrew) was David’s bible, consisting in part or all of the Pentateuch (the first five books of our bible). So when the psalm speak about ‘the law,’ ‘the decrees’ or ‘the statutes’ of God we can, for the sake of application, think of God’s written Word in general. But more than this, we should think of it not just in terms of words on a page, but the truth that is made to shine like light in our hearts by the Holy Spirit. The prayer of this psalm therefore is that we might live in the light just as John speaks of it in 1 John 1:5-10.