And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.

Wesley's Notes

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, Ge 1:14,15, and as low as the place where the birds fly for that also is called the firmament of heaven, Ge 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.

King James Translators' Notes

firmament: Heb. expansion

Scofield Reference Notes

The second day: vapor above, water below

Margin firmament

Lit. expanse (i.e. of waters beneath, of vapour above).

Jamieson-Fausset-Brown Bible Commentary

Ge 1:6-8. Second Day.

6. firmament-an expanse-a beating out as a plate of metal: a name given to the atmosphere from its appearing to an observer to be the vault of heaven, supporting the weight of the watery clouds. By the creation of an atmosphere, the lighter parts of the waters which overspread the earth's surface were drawn up and suspended in the visible heavens, while the larger and heavier mass remained below. The air was thus "in the midst of the waters," that is, separated them; and this being the apparent use of it, is the only one mentioned, although the atmosphere serves other uses, as a medium of life and light.

Matthew Henry's Concise Commentary

1:6-13 The earth was emptiness, but by a word spoken, it became full of God's riches, and his they are still. Though the use of them is allowed to man, they are from God, and to his service and honour they must be used. The earth, at his command, brings forth grass, herbs, and fruits. God must have the glory of all the benefit we receive from the produce of the earth. If we have, through grace, an interest in Him who is the Fountain, we may rejoice in him when the streams of temporal mercies are dried up.

Matthew Henry's Whole Bible Commentary

Verses 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 concerning it: 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, regions-the celestial globe, and all the spheres and 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 (v. 14, 15), and as low as the place where the birds fly, for that also is called the firmament of heaven, v. 20. When God had made the light, he appointed the air to be the receptacle and vehicle of its beams, and to be as a medium of communication between the invisible and the visible world; for, though between heaven and earth there is an inconceivable distance, yet there is not an impassable gulf, as there is between heaven and hell. This firmament is not a wall of partition, but a way of intercourse. See Job 26:7; 37:18; Ps. 104:3; Amos 9:6. 2. The creation of it. Lest it should seem as if God had only commanded it to be done, and some one else had done it, he adds, And God made the firmament. What God requires of us he himself works in us, or it is not done. He that commands faith, holiness, and love, creates them by the power of his grace going along with his word, that he may have all the praise. Lord, give what thou commandest, and then command what thou pleasest. The firmament is said to be the work of God's fingers, Ps. 8:3. Though the vastness of its extent declares it to be the work of his arm stretched out, yet the admirable fineness of its constitution shows that it is a curious piece of art, the work of his fingers. 3. The use and design of it-to divide the waters from the waters, that is, to distinguish between the waters that are wrapped up in the clouds and those that cover the sea, the waters in the air and those in the earth. See the difference between these two carefully observed, Deu. 11:10, 11, where Canaan is upon this account preferred to Egypt, that Egypt was moistened and made fruitful with the waters that are under the firmament, but Canaan with waters from above, out of the firmament, even the dew of heaven, which tarrieth not for the sons of men, Mic. 5:7. God has, in the firmament of his power, chambers, store-chambers, whence he watereth the earth, Ps. 14:13; 65:9, 10. He has also treasures, or magazines, of snow and hail, which he hath reserved against the day of battle and war, Job 38:22, 23. O what a great God is he who has thus provided for the comfort of all that serve him and the confusion of all that hate him! It is good having him our friend, and bad having him our enemy. 4. The naming of it: He called the firmament heaven. It is the visible heaven, the pavement of the holy city; above the firmament God is said to have his throne (Eze. 1:26), for he has prepared it in the heavens; the heavens therefore are said to rule, Dan. 4:26. Is not God in the height of heaven? Job 22:12. Yes, he is, and we should be led by the contemplation of the heavens that are in our eye to consider our Father who is in heaven. The height of the heavens should remind us of God's supremacy and the infinite distance there is between us and him; the brightness of the heavens and their purity should remind us of his glory, and majesty, and perfect holiness; the vastness of the heavens, their encompassing of the earth, and the influence they have upon it, should remind us of his immensity and universal providence.