At the dawn of the world, when the primordial elements were entirely intertwined, a cosmic process of order and organization took place. The separation of the upper and lower waters was not merely a physical division of matter, but the creation of a fundamental barrier that shaped the physical and spiritual structure of all reality.
A natural question arises regarding the active formation of this expanse, as God had already commanded its existence through speech. If His word alone brings the heavens into being, an additional act of formation seems redundant [רמב״ן, אור החיים, משכיל לדוד]. The primary approach among commentators is that this action does not imply creation out of nothing. Rather, it denotes a process of fixing, establishing, and perfecting. The expanse, which was initially brought forth on the first day, was now set into its final, proper form [רש״י, רמב״ן, רד״ק, בכור שור, ביאור יש״ר]. Conversely, some perspectives suggest that the terms for speaking, creating, and making are simply synonymous expressions of God's absolute will [רס״ג], or that recounting the fulfillment of a command through an action is standard biblical storytelling [קאסוטו].
The primary function of this expanse is separation. On a physical level, it serves as a barrier preventing the upper waters, which transformed into vapor, from falling and mixing with the lower waters. This division laid the groundwork for future natural phenomena like rain, snow, and hail [ספורנו, שד״ל]. Beyond the physical, this division holds profound spiritual significance. It establishes a deliberate disconnect between the material and the spiritual, allowing them to coexist as distinct entities [ביאור שטיינזלץ, אדרת אליהו]. Another view interprets this as a boundary between two forms of divine interaction: the upper waters represent direct divine providence and grace, while the lower waters represent the natural laws of the physical world [העמק דבר]. Through this process, the very nature of the waters changed; the upper waters became refined and spiritual, while the lower waters remained entirely physical [מלבי״ם].
Notably, the upper waters do not physically rest upon the expanse. Instead, they remain suspended in the space above it, held in place purely by the power of God's word. This suspension defies natural law and stands as a profound, miraculous innovation in the fabric of creation [רש״י, מזרחי, גור אריה, דברי דוד, חתם סופר]. The establishment of this reality is then confirmed with a declaration that it was so. Uniquely, this confirmation appears after the description of the action, rather than immediately following God's initial command, as it does on other days of creation. This placement emphasizes the eternal permanence of this new natural order. Even though suspending water in the air contradicts physical laws, this miraculous state was fixed and preserved for all time [רמב״ן, ספורנו, רד״ק, חזקוני]. A differing view connects this confirmation to the subsequent naming of the expanse, suggesting that once the state was firmly established as planned, God then named it Heaven [אבן עזרא].
The events of the second day naturally raise a famous question regarding why there is no declaration that the creation was "good." The primary consensus is that the work involving the waters was simply incomplete. It was not finished until the third day, when the waters were gathered to reveal dry land. Because an unfinished work cannot be considered entirely perfect or good, the declaration was delayed until the third day. Consequently, the third day features two declarations of goodness: one for completing the separation of the waters, and a second for the creation of the land [רש״י, מזרחי, בכור שור]. Other explanations suggest that the very concept of separation carries connotations of division, conflict, and jealousy between the upper and lower waters. Furthermore, a tradition notes that the fires of Hell were created on the second day. Therefore, it was not an appropriate moment for complete joy or a declaration of absolute goodness [רס״ג, חזקוני, ברכת אשר, יריעות שלמה].