Naming the firmament marks a critical transition in creation, defining the physical boundaries of the universe and assigning them a distinct purpose. By establishing the heavens, a structured space is formed to mediate between the upper spiritual realms and the earthly domain. The divine act of naming is not merely assigning a title; it is the process of embedding the very essence and nature into the creation [מלבי״ם]. God personally named five primordial elements, namely light, darkness, heaven, earth, and the seas, because humanity had not yet been created to perform this task [אבן עזרא]. This naming also reflects His absolute mastery over the heavens, demonstrating His exclusive authority to grant or withhold rain, a power entirely beyond human control [שד״ל].
Although the heavens are mentioned at the very beginning of creation, the primary approach among commentators is that this initial reference was made in anticipation of the future, with the actual naming occurring only on the second day [רמב״ן, אור החיים]. A clear distinction exists between the heavens of the first day and the firmament of the second. The original heavens represent the upper, spiritual realm, home to the divine throne and the angels. In contrast, the firmament created on the second day is the lower physical atmosphere. God applied the name "heaven" to this firmament as a borrowed term from the spiritual realm above [רמב״ן, הכתב והקבלה, ביאור יש״ר]. Its primary function is to serve as a mediating screen, channeling heavenly influences and light down to Earth [ספורנו, רש״ר הירש].
The name chosen for the heavens carries profound conceptual meaning. The primary approach among commentators identifies three complementary ideas: it is the entity that carries the upper waters, the location where water is formed and from which rain descends, and a miraculous blend of the opposing elements of fire and water [רש״י, גור אריה, לבוש האורה, רד״ק]. Others suggest the root of the word simply points to a distant, elevated place [הכתב והקבלה, ביאור שטיינזלץ]. On a deeper level, God specifically chose the name "heaven" rather than retaining the term "firmament." While a firmament symbolizes a screen that divides and separates, the concept of heaven, forged from fire and water, represents peace and perfect harmony between conflicting forces [כלי יקר].
A striking feature of the second day of creation is the absence of the divine declaration that it was good. The most prominent explanation is that the work involving the waters was not completed until the third day, and something unfinished cannot be deemed truly good [רש״י, תורה תמימה, מלבי״ם, קאסוטו]. Furthermore, this day introduced division and separation into the world, whereas perfect goodness can only exist in a state of unity [כלי יקר, הדר זקנים]. Other traditions suggest the declaration was omitted because the fires of hell were created on this day, and because God foresaw that He would one day use floodwaters to bring destruction to the world [הדר זקנים, תורה תמימה, חומש קה״ת].
The conclusion of the day establishes the biblical definition of a full day as a cycle beginning as the afternoon leans toward evening and continuing until the following evening [רשב״ם, חומש קה״ת]. At this moment, creation entered a measurable framework of time [ביאור שטיינזלץ]. The designation of the second day simply reflects its ordinal position in the sequence of creation. The Torah does not grant independent names to the days of the week; instead, it counts each one solely in its relation to the upcoming Sabbath [תורה תמימה].