Knowest thou the ordinances of heaven? - The laws or statutes by which the motions of the heavenly bodies are governed. These were wholly unknown in the time of Job, and the discovery of some of those laws - for only a few of them are yet known - was reserved to be the glory of the modern system of astronomy. The suggestion of the great principles of the system gave immortality to the name Copernicus; and the discovery of those laws in modern times has conferred immortality on the names of Brahe, Kepler, and Newton. The laws which control the heavenly bodies are the most sublime that are known to man, and have done more to impress the human mind with a sense of the majesty of God than any other: discoveries made in the material universe. Of course, all those laws were known to God himself, and he appeals to them in proof of his greatness and majesty. The grand and beautiful movements of the heavenly bodies in the time of Job were fitted to produce admiration; and one of the chief delights of those that dwelt under the splendor of an Oriental sky was to contemplate those movements, and to give names to those moving lights. The discoveries of science have enlarged the conceptions of man in regard to the starry heavens far toward immensity; have shown that these twinkling lights are vast worlds and systems, and at the same time have so disclosed the laws by which they are governed as to promote, where the heart is right, intelligent piety, and elevate the mind to more glorious views of the Creator.
Canst thou set the dominion thereof in the earth? - That is, “dost thou assign the dominion of the heavens over the earth?” The reference is, undoubtedly, to the influence of the heavenly bodies upon sublunary objects. The exact extent of that cannot be supposed to have been known in the days of Job, and it is probable that much more was ascribed to the influence of the stars on human affairs than the truth would justify. Nor is its extent now known. It is known that the moon has an influence over the tides of the ocean; it may be that it has to some extent over the weather; and it is not impossible that the other heavenly bodies may have some effect on the changes observed in the earth which is not understood. Whatever it is, it was and is all known to God, and the idea here is, that it was a proof of his immense superiority over man.