בראשית, פרק א׳, פסוק י״ד

On the fourth day of creation, the world transitions from a state of abstract, primordial light into an organized system of time and nature. The primary consensus among commentators is that the celestial bodies are not created out of nothing on this day. Rather, the original spiritual light brought forth on the first day is now concealed, concentrated, and poured into physical vessels—the sun, the moon, and the stars. God then commands these vessels to be suspended in the firmament that was formed on the second day [רש״י, רמב״ן, רד״ק, אברבנאל, שד״ל, הכתב והקבלה]. They are fixed within the thickness of the celestial sphere, moving along with it much like nails driven into the hull of a moving ship [רבנו בחיי, תולדות יצחק].

The emergence of these celestial bodies carries an underlying theme of lack or diminishment, subtly indicated in the original text through a deficient spelling that connects them to the concept of a curse or loss. This conveys several profound ideas. First, it alludes to the diminishment of the moon. Originally created equal in size to the sun, the moon was reduced after arguing that two kings cannot share a single crown [בעל הטורים, אור החיים, צאינה וראינה]. Second, because these bodies are the creators of time, they inherently bring about a reality where everything bound by time is subject to decay, sorrow, and loss [כלי יקר]. Additionally, this concept of lack serves as a subtle warning regarding a throat disease that historically endangered children on the fourth day of the week, prompting a custom in earlier generations to fast on Wednesdays [רש״י, מנחת שי, תורה תמימה].

The primary role of these newly formed bodies is to separate the day from the night. During the first three days of creation, light and darkness operated and alternated solely through God's direct command. Now, with the natural order established, the task of separation is delegated to the luminaries. They function as God's dedicated servants, operating according to fixed, predictable laws [שד״ל, רד״ק].

Beyond simple illumination, these bodies serve as signs, a function understood in complementary ways. On one hand, they act as omens through unusual phenomena like solar and lunar eclipses or the appearance of comets. While the ancient world viewed such events with dread, the sages emphasize that when the people of Israel fulfill God's will, they have nothing to fear from the heavens [רש״י, רמב״ן, רבנו בחיי, אברבנאל]. Conversely, designating them as signs serves to actively uproot pagan beliefs in astrology. They are not independent deities dictating the future, but merely components of the natural order established by God [שד״ל]. On a practical level, they also act as daily markers for fulfilling time-bound Commandments, such as the morning and evening prayers [רבנו בחיי].

Finally, the celestial bodies establish a permanent natural calendar to organize human life, defining recurring seasons, days, and years. They dictate the agricultural and climatic shifts—summer, winter, planting, and harvest—driven by the sun's tilt [רמב״ן, רד״ק, מלבי״ם], as well as the religious festivals of Israel, which follow the cycle of the moon's renewal [רשב״ם, שד״ל, חזקוני]. Their movements define the fundamental units of time: the twenty-four-hour cycle of day and night [רש״י, רמב״ן, רד״ק], the full 365-day solar year as the sun completes its circuit through the zodiac, and the lunar year [רד״ק, אברבנאל].