The establishment of the celestial bodies sets the foundation for time and natural order in the physical world. These bodies are given a dual purpose: to govern and to separate. On a basic level, the sun takes charge of the day, while the moon directs the night [רד"ק, בכור שור]. Even though the moon is occasionally visible during the day, it exerts no influence then, appearing merely like a candle lit in broad daylight [בכור שור, חזקוני]. The focus of this governance is on the periods of day and night themselves, rather than a direct rule over the earth's inhabitants [שד"ל].
In the physical realm, this governance translates into a very real and direct impact on the earth. The sun operates through heat and dryness to stimulate plant growth, while the moon functions through cold and moisture to influence the oceans and springs [רמב"ן, הטור הארוך, רבנו בחיי, מלבי"ם]. Together, they regulate the climate, agricultural cycles, and the rhythm of human life [ר' סעדיה גאון]. On a spiritual level, God granted these bodies the power to influence earthly events, yet they remain strictly His agents, operating solely through His power. This distinction is crucial, designed to prevent humanity from falling into the trap of idol worship [רמב"ן, רבנו בחיי, ר' סעדיה גאון, מחוקקי יהודה]. Furthermore, the concept of governance mirrors mankind's own purpose to master the physical world and elevate it spiritually through the Torah [חומש קה"ת].
Regarding the second role of separating light from darkness, a natural question arises: how can objects that emit light create a division between light and darkness? The primary approach among commentators is that this refers to setting the boundaries of time. Sunrise marks the beginning of light, and the appearance of the stars marks the beginning of darkness [רשב"ם, אבן עזרא, רד"ק]. In this context, light and darkness are essentially synonyms for day and night, concepts that were established at the very beginning of creation [רמב"ן, הטור הארוך, קאסוטו, מחוקקי יהודה]. While day and night previously existed in an abstract sense, they are now firmly defined and visible to everyone [ביאור שטיינזלץ].
Other perspectives offer different nuances to this separation. Some suggest that the division is actually carried out by the stars, which emerge the moment the light fades [חזקוני]. Others explain that the distinction lies in the quality of the light itself. Sunlight is powerful enough to pierce through clouds, ensuring the day remains bright, whereas cloud cover over the moon results in total darkness [העמק דבר]. Ultimately, this separation of light and darkness is a reality only from the perspective of the earth, as light remains constant in the vastness of space [מלבי"ם].
The divine recognition of this creation as good reflects the immense benefit and order these celestial bodies bring to the world, enabling humanity to calculate times, seasons, and natural cycles [ר' סעדיה גאון, רבנו בחיי]. Moreover, the act of condensing the initial, boundless spiritual light of early creation into a physical sun was a positive and necessary step. It was precisely tailored to meet the physical needs of the animals and humans who were soon to be brought into existence [מלבי"ם].