The day is thine, the night also is thine. The prophet now descends to the consideration of the divine benefits which are extended in common to all mankind. Having commenced with the special blessings by which God manifested himself to be the Father of his chosen people, he now aptly declares that God exercises his beneficence towards the whole human family. He teaches us, that it is not by chance that the days and nights succeed each other in regular succession, but that this order was established by the appointment of God. The secondary cause of these phenomena is added, being that arrangement by which God has invested the sun with the power and office of illuminating the earth; for after having spoken of the light he adds the sun, as the principal means of communicating it, and, so to speak, the chariot in which it is brought when it comes to show itself to men. As then the incomparable goodness of God towards the human race clearly shines forth in this beautiful arrangement, the prophet justly derives from it an argument for strengthening and establishing his trust in God.

The day is thine, the night also is thine - Thou hast universal dominion. All things are under thy control. Thou hast power, therefore, to grant what we desire of thee.
Thou hast prepared the light and the sun - He who has made the sun - that greatest and noblest object of creation to the view of man - must have almighty power, and must be able to give what we need.

The day is thine, the night also is thine - Thou art the Author of light, and of the sun, which is the means of dispensing it.

The (m) day [is] thine, the night also [is] thine: thou hast prepared the light and the sun.
(m) Seeing that God by his providence governs and disposes all things, he gathers that he will take care chiefly for his children.

The day is thine, and the night also is thine,.... He made the one and the other, and divided the one from the other; and can make them longer or shorter, clear or cloudy, as he pleases: and the day of prosperity and night of adversity are at his disposal; all the times of his people and of his church are in his hands; sometimes it is a night of darkness, deadness, sleepiness, and security, as it now is; ere long there will be no more night, but bright day; the light of the moon will be as the light of the sun, and the light of the sun will be seven fold as the light of seven days; and this is to be expected from him whose is the day and the night also, Revelation 21:25. Jarchi interprets the day, of the redemption of Israel; and the night, of distresses and afflictions:
thou hast prepared the light and the sun; first the light, and then the sun; for the light was before the sun; or the luminary, even the sun. Aben Ezra interprets the "light" of the moon, and so the Targum; and Kimchi, both of the moon and of the stars; Jarchi takes the light figuratively to be meant of the light of the law; but it is much better to understand it of the light of the Gospel, which God has prepared, and will send forth more largely in the latter day, whereby the whole earth shall be lightened; and when Christ the "sun" of righteousness will arise with healing in his wings, and who gives both the light of grace and glory to his people.

The fixed orders of nature and bounds of earth are of God.

The light - The moon, the lesser light.