Then called God to the expanse, heaven. - This expanse is, then, the proper and original skies. We have here an interesting and instructive example of the way in which words expand in their significance from the near, the simple, the obvious, to the far and wide, the complex and the inferential: The heaven, in the first instance, meant the open space above the surface in which we breathe and move, in which the birds fly and the clouds float. This is the atmosphere. Then it stretches away into the seemingly boundless regions of space, in which the countless orbs of luminous and of opaque surfaces circumambulate. Then the heavens come to signify the contents of this indefinitely augmented expanse, - the celestial luminaries themselves. Then, by a still further enlargement of its meaning, we rise to the heaven of heavens, the inexpressibly grand and august presence-chamber of the Most High, where the cherubim and seraphim, the innumerable company of angels, the myriads of saints, move in their several grades and spheres, keeping the charge of their Maker, and realizing the joy of their being. This is the third heaven 2-Corinthians 12:2 to the conception of which the imaginative capacity of the human mind rises by an easy gradation. Having once attained to this majestic conception, man is so far prepared to conceive and compose that sublime sentence with which the book of God opens, - "In the beginning God created 'the heavens' and the earth."
The expanse, or aerial space, in which this arrangement of things has been effected, having received its appropriate name, is recognized as an accomplished fact, and the second day is closed.

And God called the firmament (g) Heaven. And the evening and the morning were the second day.
(g) That is, the region of the air, and all that is above us.

And God called the firmament heaven,.... Including the starry and airy heavens: it has its name from its height in the Arabic language, it being above the earth, and reaching to the third heaven; though others take the word "shamaim" to be a compound of two words, "sham" and "maim", that is, there are waters, namely, in the clouds of heaven:
and the evening; and the morning were the second day; these together made up the space of twenty four hours, which was another natural day; the body of light, created on the first day, having again moved round the chaos in that space of time; or else the chaos had turned round on its own axis in that time, which revolution produced a second day; and which, according to Capellus, was the nineteenth of April, and according to Bishop Usher the twenty fourth of October. It is an observation that everyone may make, that the phrase,
and God saw that it was good, is not used at the close of this day's work, as of the rest: the reason some Jewish writers give is, because the angels fell on this day; but it is a much better which Jarchi gives, and that is, because the work of the waters was not finished; it was begun on the second day, and perfected on the third (d); and therefore the phrase is twice used in the account of the third day's work: the Septuagint version adds it here indeed, but without any foundation.
(d) Vid. Maimon. Moreh Nevochim, par. 2. c. 30.