With ver. 19 the psalmist passes to the fourth day, but thinks of moon and sun only in relation to the alternation of day and night as affecting creatural life on earth. The moon is named first, because the Hebrew day began with the evening. It is the _measurer_, by whose phases seasons (or, according to some, _festivals_) are reckoned. The sun is a punctual servant, knowing the hour to set and duly keeping it. "Thou appointest darkness and it is night." God wills, and His will effects material changes. He says to His servant Night, "Come," and she "comes." The psalmist had peopled the vales and mountains of his picture. Everywhere he had seen life fitted to its environment; and night is populous too. He had outlined swift sketches of tame and wild creatures, and now he half shows us beasts of prey stealing through the gloom. He puts his finger on two characteristics--their stealthy motions, and their cries which made night hideous. Even their roar was a kind of prayer, though they knew it not; it was God from whom they sought their food. It would not have answered the purpose to have spoken of "all the loves, Now sleeping in those quiet groves." The poet desired to show how there were creatures that found possibilities of happy life in all the variety of conditions fashioned by the creative Hand, which was thus shown to be moved by Wisdom and Love. The sunrise sends these nocturnal animals back to their dens, and the world is ready for man. "The sun looked over the mountain's rim," and the beasts of prey slunk to their lairs, and man's day of toil began--the mark of his pre-eminence, God's gift for his good, by which he uses creation for its highest end and fulfils God's purpose. Grateful is the evening rest when the day has been filled with strenuous toil. The picture of earth and its inhabitants is now complete, and the dominant thought which it leaves on the psalmist's heart is cast into the exultant and wondering exclamation of ver. 24. The variety as well as multitude of the forms in which God's creative idea is embodied, the Wisdom which shapes all, His ownership of all, are the impressions made by the devout contemplation of Nature. The scientist and the artist are left free to pursue their respective lines of investigation and impression; but scientist and artist must rise to the psalmist's point of view, if they are to learn the deepest lesson from the ordered kingdoms of Nature and from the beauty which floods the world.