בראשית, פרק א׳, פסוק י״ז

The placement of the celestial bodies in the sky marks the moment they receive their permanent and practical roles within creation. After their initial formation, the focus shifts to their exact location, their purpose, and their ongoing relationship with the earth.

The primary approach among commentators is that this action represents a physical placement and establishment. Although the lights were created on the very first day, it was only on the fourth day that God permanently fixed them in their proper positions [רד״ק, ברטנורא, שד״ל]. They were initially formed outside the sky and were subsequently brought inside [יהל אור], with the firmament acting as a vast storehouse where they remain securely anchored [תורה תמימה, קרני אור].

Beyond physical location, this placement also signifies an appointment of power. God granted the lights the official authority to govern the day and the night [מלבי״ם, יהל אור], much like the later placement of the rainbow as a lasting symbol [אבן עזרא, יהל אור]. Alternatively, this act is viewed as an absolute, unconditional gift from God to the world. The celestial bodies are not independent beings. They are strictly obligated to illuminate the earth continuously and cannot gather up their light or refuse to shine, even if humanity behaves corruptly [אור החיים].

Regarding their purpose to illuminate the earth, there is a clear distinction between their various functions. Shining simply refers to the spreading of light, while ruling relates to their active influence over the world [רד״ק]. Chronologically, the moment God suspended the lights in the sky, they immediately began to shine. However, their ability to rule only took effect once they began moving along their designated orbits, and the actual separation between light and darkness occurred only later, as evening fell [העמק דבר]. This separation was designed to establish firm boundaries, ensuring that each light remains strictly within its own domain without encroaching on the territory of the other [אור החיים].

Interestingly, the sequence of these functions during the actual execution presents a mirrored structure to the original divine plan. While the initial instruction at the start of the fourth day dictated that the lights should first separate, then rule, and finally shine, the actual fulfillment unfolds in reverse. They first shine, then rule, and ultimately separate [קאסוטו].