Why does the Bible describe the moon as a light?

The work of the fourth day has presented difficulties to many; partly because years ago, under mistaken scientific ideas, light (v. 3) without the sun (v. 16) was regarded as an impossibility; partly because men did not carefully note what verses 14 to 18 really do say, and do not say Sun and moon were created as given us in verse 1; they were only made as "two great lights" on the fourth day; and, further, they were so set in relation to the earth, or the earth to them, as the case may be, that they ruled over the day and over the night, dividing the light from the darkness.

It is assuredly not the creation of the sun, etc. This the inspired historian does not say, but only that God now constituted the heavenly luminaries, after the plants and before the animals for the Adamic earth. Light had shone otherwise since the first day of the great week. Now He set the light-bearers of the heavens to do their assigned work, but it is for the earth, and indeed for man. Their creation was implied in ver. 1; for God did not create either empty; and what would heaven be without its host? And we saw that ver. 2 implies that the earth even had not been so, though so it became with other marks of disorder. What then hindered the functions of sun and moon was now rectified. Light independently had been proved to be under God's control. On the fourth day He gave the luminaries of heaven their unhindered relation to divide the day from the night. Now we can readily understand the plants (and these were for the use of man and his congeners) caused to spring forth on the day before without the sunbeam; but assuredly not so of a geological age of grass, corn, and fruit. Yet we see the fitness of the due ordering of light and heat, as we have it, the next day, if the plants were to flourish, as well as for the animal life that begins after that according to His word.

110 I believe fully God set at this time the sun and the moon to be for signs and seasons and years, and to make day and night; but they are viewed here solely in this aspect towards the earth, and only as lights. God made the two great lights, eth shenee hameoroth, and God gave them as such. There is no creation of the bodies. There is the establishment of the phenomena, and their purpose. Hence, when he speaks of the stars, he only takes care to remind us, that God had made them too. Instead of men's worshipping them, God had distributed them to all men under heaven; but, as not having any other place with this earth, it is simply left in that way.

Verse 14 is remarkable in this, that God does not make the sun and moon, "and it was so," but, as with the light, "God said, let there be lights"; in whatever way, He made them appear as centres of light to the earth, He set them for the seasons, and signs of the earth, and it was so. And God made all these lights, and the stars, and set or gave them to light the earth and rule, etc.; and God saw that it was good.

Again, on the fourth day we hear of the luminaries. And here mark the consistency and propriety of the language. It is not said that God then created them, but simply, "Let there be lights in the firmament." It is not light now, but "lights," or light-bearers, "in the firmament of the heaven, to divide the day from the night; and let them be for signs, and for seasons, and for days, and years: and let them be for lights in the firmament of the heaven, to give light upon the earth: and it was so. And God made two great lights; the greater light to rule the day, and the lesser light to rule the night (the stars also)." These last are just referred to, and it was the more important because, as is generally known, many of those that had the greatest weight in the ancient world adored the stars. Even Plato, although a western, was sufficiently tinctured by orientalism to yield to the monstrous figment that the earth is a sort of living creature. As the philosophy of Aristotle directly tended to atheism (for it was low-minded empiricism), so the philosophy of Plato led into, if it was not downright, pantheism. Such was the difference between them. Pantheism, though in sound opposed, is really near akin to atheism.

It has been thought by some that light was independent of the sun, that on the first day God created the light, and that on the fourth day He created the sun. But we are not told that on the fourth day He created the sun and the moon, but that He made two great lights. We believe that the sun and moon were created at the first, and were included in the statement that in the beginning God created the heaven and the earth. What proves this, we believe, is the statement that the evening and the morning were the first day, proving the diurnal motion of the earth, in relation to the sun, resulting in day and night.

We are told these two lights were for signs and seasons and days and years. They are God’s great timekeepers. Every day they are signs to mankind. They declare the Creator’s “eternal power and Godhead” (Rom. 1:20). In the wonderfully vivid and beautiful language of Psalm 19, the heavens declare the glory of God. Day by day utters speech. Night by night shows knowledge. Its speech is known by all mankind. In the heavens has He set a tabernacle for the sun, which as a bridegroom coming out of his chamber, rejoices as a strong man to run a race.

Most certainly those in the physical universe proceeded from Him, for "God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs and for seasons, and for days and years… He made the stars also. And God set them in the firmament of the heaven to give light upon the earth" (Gen. 1:14-17). We see the wisdom and kindness of our faithful Creator in these lights above us and we enjoy them and give thanks for them. Life would be impossible without them; they bring order and method and variety and guidance into our lives, and he who would live well and long must not ignore "the signs and seasons and days and years" for which these lights were made. The shipmaster steers his vessel with safety, if he can take his bearings by the lights in the heaven; many a gallant ship has been lost because steered by dead reckoning. Those lights proceeded from God to guide the mariner over tempestuous seas.

On the fourth day we have the setting of the sun and the moon in their appointed places in relation to the earth. Besides the sun being the source of heat, the ripener of the harvests, the power for evaporation in order that rain might descend on the earth, we are told it is to rule the day, and the moon to rule the night.

These lights were "for signs and for seasons and for days and years." As well as their introducing each succeeding day, they have a significance more important than their being an actual literal blessing. Their changing positions at different times of the year also indicates the changing seasons on earth. Then when all the seasons have passed through their yearly cycle, the position of the sun and moon marks the beginning of another year.

You see where those are that speak about the enormous length of time necessary for light to be transmitted — though this again is more than they ought to assume — at any rate for the action of light by means of the heavenly orbs. But there is no difficulty whatever. When God created the heavens, did He make them empty? Did He not create also the host of heaven? What about the sun, and moon, and stars? He created them some time. That they were made we find elsewhere in this chapter; not, I presume, the absolute moment of their creation, but of their being made to serve for the use of man on the earth. What other uses they served we are not there informed. That they were God's handiwork, and for man's use, as creatures of God here below — not objects of worship, as in heathenism, He does explain. Surely there was wisdom in saying this and no more. There was considerate goodness in what He said, and in what He withheld.