The creation process advances from a state of formless chaos to an ordered reality through a deliberate act of separation. The primordial waters that once encompassed everything are split into two distinct entities, opening up the space necessary for the physical world to exist. This systematic, physical progression stands in stark contrast to ancient mythologies that depicted the formation of heaven and earth as the fallout of violent battles between gods and monsters [קאסוטו]. The expanse forged during this process is characterized as something stretched out and flattened, much like a pitched tent canvas or a sheet of beaten metal [רשב״ם, אבן עזרא, שד״ל, רמב״ן, רד״ק, הטור, קאסוטו].
The exact nature of this expanse is viewed through several different lenses. One approach identifies it as the Earth's atmosphere, the space where clouds, rain, and weather patterns take shape [אבן עזרא, שד״ל, רד״ק, מלבי״ם, יש״ר, רש ר הירש]. Another perspective understands it as the vast celestial spheres where the stars are fixed [ספורנו, מזרחי, רלב״ג, אברבנאל]. A third tradition suggests that the heavens were actually brought into existence on the first day but remained in a fluid, unstable state; the divine decree on the second day served to solidify and stabilize them [רש״י, רמב״ן, ברטנורא, תורה תמימה, שפתי חכמים, לבוש האורה, חזקוני]. Alternatively, the expanse might not be a tangible physical object at all, but rather an optical illusion that creates the appearance of a blue sky [קונטרס חיבה יתירה].
The placement of this expanse is set amidst the waters. The primary approach among commentators is that it sits at the exact mathematical center, creating an equal distance between the waters on Earth and the waters above [רשב״ם, רמב״ן, מזרחי, גור אריה, רש״י, תורה תמימה]. However, another view suggests it merely acts as a partition between the two bodies of water, even if it is closer to one than the other [לבוש האורה]. The suspension of the upper waters above this expanse is a subject of profound contemplation. Many understand it as a continuous miracle; the waters do not rest on a physical surface but are suspended in midair contrary to the laws of nature, held in place purely by God's decree [רמב״ן, רד״ק, מזרחי, רלב״ג, תורה תמימה, צאינה וראינה, רש״י]. This division was executed with hairsbreadth precision, demonstrating a divine exactness impossible for humanity to replicate [תורה תמימה, אברבנאל]. Conversely, a more naturalistic approach explains the upper waters simply as vapor and clouds, operating within the standard meteorological laws of evaporation and rain that God embedded into the world [שד״ל, רד״ק, מלבי״ם, רש ר הירש].
Beyond the physical architecture of the universe, this separation carries deep spiritual significance. The upper waters represent divine kindness, spiritual influence, and masculine energy, while the lower waters symbolize strict justice, receptivity, and feminine energy [רקנאטי, צרור המור, מלבי״ם, נחלת יעקב]. There is also a profound moral lesson embedded in the boundaries established on this day. Initially, the heavens and waters expanded boundlessly until God commanded them to stop and hold their positions. Human nature similarly drives people to expand their desires and actions without limit. Just as God established physical boundaries in creation, humanity must learn to pause and establish moral boundaries through divine law [כלי יקר].
Notably, the second day of creation is the only one where God does not declare that the work was "good." The primary reason for this omission is that the manipulation of the waters was not actually completed until the third day; thus, the declaration of goodness awaited the finished product [רשב״ם, רלב״ג, צאינה וראינה, אלשיך]. Other explanations tie this absence to the very nature of the day's work: the act of separation introduced division and conflict into the world, and nothing good can inherently emerge from discord. Furthermore, some traditions note that this was the day Hell was created, casting a shadow over the proceedings [כלי יקר, רלב״ג, צאינה וראינה, אברבנאל].