John Calvin Commentary Psalms 19:2

"Day unto day uttereth speech, And night unto night showeth knowledge." — Psalms 19:2 (ASV)

Day unto day uttereth speech. Philosophers, who have more insight into those matters than others, understand how the stars are arranged in such beautiful order that, despite their immense number, there is no confusion; but to the ignorant and uneducated, the continual succession of days is a more certain proof of the providence of God.

David, therefore, having spoken of the heavens, does not here descend from them to other parts of the world; but, from an effect more perceptible and more easily grasped by us, he confirms what he has just said, namely, that the glory of God not only shines but also resounds in the heavens.

The words may be interpreted in various ways, but the different interpretations that have been given of them make little difference to the meaning. Some explain them in this way: that no day passes in which God does not show some striking evidence of His power. Others believe that they signify increases in instruction and knowledge—that every following day contributes something new as proof of the existence and perfections of God.

Others view them as meaning that the days and nights talk together and discuss the glory of their Creator, but this is a somewhat forced interpretation. David, I have no doubt, here teaches from the established alternations of days and nights that the course and revolutions of the sun, moon, and stars are regulated by the marvelous wisdom of God.

Whether we translate the words Day after day, or one day to another day, is of little consequence, for all that David means is the beautiful arrangement of time that the succession of days and nights brings about. If, indeed, we were as attentive as we ought to be, even one day would be enough to testify to us of the glory of God, and even one night would be sufficient to serve the same purpose for us.

But when we see the sun and the moon performing their daily revolutions—the sun by day appearing over our heads, and the moon following in its turn; the sun ascending by degrees, while at the same time approaching us more closely, and afterwards bending its course to depart from us gradually—and when we also see that in this way the length of the days and nights is regulated, and that the variation of their length is arranged according to such a uniform law that it invariably recurs at the same points of time in every following year, we then have in this a much clearer testimony to the glory of God.

David, therefore, with excellent reason, declares that even if God were not to speak a single word to humans, the orderly and useful succession of days and nights eloquently proclaims the glory of God, and that there is now left to humans no pretext for ignorance. For since the days and nights serve us so well and so carefully as teachers, we may acquire, if we are sufficiently attentive, a sufficient amount of knowledge from their teaching.