Psalm 19 is a wisdom psalm in which David praises God's creation and instruction. David calls attention to the heavens because the sun, the moon, and the stars declare the Creator's glorious activity. The radiance of the sun and the orderly appearance of the moon and stars bear witness to the existence of a Master Designer (see also Romans 1:20).

Verse 4 of Psalm 19 reads variously, "their line has gone out" (perhaps meaning orbit) and "their voice goes out" (NRSV). Even in English, the word "line" can denote a geometric line, a line of text or the text an actor is given to speak aloud. David mentions that the voice of the celestial bodies can be heard everywhere (verse 3). "The poem talks of hearing the glory of God. It declares that behind the whole majesty of nature there is sound, the sound of the Word of God. The whole creation, even without the use of words, sounds forth the divine Word; when put into Greek, this is the word Logos that we meet in John 1:1" (George Knight, Psalms, The Daily Study Bible Series, comments on Psalm 19:1-6).

Some see in these verses the idea that, prior to His written revelation in Scripture, God formed the constellations to communicate the story of His plan for humanity—imagery that was corrupted in pagan mythology (see, for instance, E.W. Bullinger's book The Witness of the Stars and E. Raymond Capt's book The Glory of the Stars). Yet even apart from that, the heavens certainly have a powerful message to communicate. As verse 1 shows, they demonstrate the sublime majesty, creativity, genius and power of God.

David compares the sun to a bridegroom, cheerfully leaving his chamber, and to the strength of a champion prepared for his race. "Nothing," he adds, "is hidden from the sun's radiance and strength," just as nothing is hidden from the glory of God. It is interesting to consider that in the New Testament, Jesus Christ, God the Word made flesh, is referred to as both the "bridegroom" (Matthew 25:1-10) and the "light of the world" (John 8:12)—His followers also have this latter distinction through reflecting the "light" of His character (Matthew 5:14).

Just as God (both Father and Son) is brilliant in glory and illuminating, so also is God's law. Indeed, the psalm now moves from the heavenly revelation to the written revelation of God. The word "law" is translated from the Hebrew torah and means instruction (verses 7-10). "This portion of the psalm "presents six words for the law of God—law, testimony, statutes, commandment, fear, and judgments; six evaluations of the law—perfect, sure, right, pure, clean, and true; and six results—converting the soul, making wise the simple, rejoicing the heart, enlightening the eyes, enduring forever, and righteous altogether" (Nelson Study Bible, note on vv. 7-10). Curiously, the terms here are thoroughly elaborated on exactly 100 psalms later—in Psalm 119.

Consideration of God's majesty as revealed in the heavens and the stark perfection of His law, David is reminded of his own inadequacies. He asks a searching question, "Who can understand his [own] errors?" (verse 12). God says that a man's heart is desperately wicked and that only He really understands it (Jeremiah 17:9). Since a man can't get to the bottom of his nature and rid himself of his faults, God must intervene to forgive him of his shortcomings and help him to obey (Psalm 19:12). God's power can enable us to stay away from deliberate sins and reveal the secret faults over the course of our years of seeking to follow His way of life (verse 13; 139:23-24).

David prays that his words and thoughts will be pleasing in God's sight, similar to the request he makes in Psalm 141:3: "Set a guard, O Lord, over my mouth; keep watch over the door of my lips." Such a "guard" is the Holy Spirit reminding us of right and wrong, which we learn from our study of God's Word. The Spirit helps us to do what we should. But the choice to do the right and the effort to control the lips remains up to us.