Genesis 1:7

Firmament - Expanse or vault over the earth; sky.

Then made God the expanse. - Here the distinction between command and execution is made still more prominent than in the third verse. For the word of command stands in one verse, and the effect realized is related in the next. Nay, we have the doing of the thing and the thing done separately expressed. For, after stating that God made the expanse, it is added, "and it was so." The work accomplished took a permanent form, in which it remained a standing monument of divine wisdom and power.

1:6-8 We have here an account of the second day's work, the creation of the firmament. In which observe, 1. The command of God; Let there be a firmament - An expansion; so the Hebrew word signifies, like a sheet spread, or a curtain drawn out. This includes all that is visible above the earth, between it and the third heavens, the air, its higher, middle, and lower region, the celestial globe, and all the orbs of light above; it reaches as high as the place where the stars are fixed, for that is called here the firmament of heaven, Genesis 1:14,15, and as low as the place where the birds fly for that also is called the firmament of heaven, Genesis 1:20. 2. The creation of it: and God made the firmament. 3. The design of it; to divide the waters from the waters-That is, to distinguish between the waters that are wrapt up in the clouds, and those that cover the sea; the waters in the air, and those in the earth. 4. The naming it; He called the firmament Heaven - 'Tis the visible heaven, the pavement of the holy city. The height of the heavens should mind us of God's supremacy, and the infinite distance that is between us and him; the brightness of the heavens, and their purity, should mind us of his majesty, and perfect holiness; the vastness of the heavens, and their encompassing the earth, and influence upon it, should mind us of his immensity and universal providence.