What does it mean that God saw that it was good (Genesis 1:18)?

This, again, as definitely excludes scientific preoccupation as it confirms the reference throughout. The stars only come in parenthetically. God made them too, if blind man deified them. But God gave sun and moon to rule over the day and over the night. They were His creatures and gifts for man's use dividing between the light and the darkness. "And God saw that [it was] good," not as if they were just created, but in the assigned work He gave to be done by them. "And there was evening and there was morning, a fourth day." Here it cannot be fairly denied by any, that from the necessary effect of that day's work we have the ordinary vicissitude of night and day; and that a similar diurnal revolution followed for the fifth and sixth days, as for every day since, including the seventh. But this being so, surely consistency requires it for the three previous days. That light was supplied otherwise before the fourth day is no impediment. The daily course of the earth on its axis depends on gravitation, not on illumination, and would have gone on equally, had the sun been only and always opaque, or had its previous and its present action in light-bearing never existed.

God saw the light that it was good. He divided the light from the darkness, calling the light Day, and the darkness Night.

It is significant that God speaks of the Day first and then of the Night. He calls the light good, not the darkness.

Hence "creation" of light, first or second, in the universe is only the slip of philosophers. Scripture is more accurate than its most modern expounder, even when striving to show the accordance of science with the Bible. In the gloom that overhung the earth thrown into desolation God caused light to act, as the characteristic act of the "first day" of the week, the brief cycle that was to close with man its new master and representative of God here below. "And God saw the light that [it was] good; and God divided the light from the darkness; and God called the light Day, and the darkness he called Night." It presents to us God pondering and speaking in gracious consideration of the race He was about to create thereon, with a mind dwelling on realities about to open out for man far more solemn than the light or the darkness, day or night, literally. Yet the light of the eyes rejoices the heart, says the Preacher (Prov. 15:30), and truly is sweet (Eccles. 11:7), as God pronounced it "good." "And it was evening, and it was morning, first (or, one) day." Only we must guard against taking the previous darkness as the evening. It would appear rather that light shone; and then its waning into night, and brightening into day, constituted the first day. That the earth would revolve on its axis, before the light-bearing of the sun afterwards, and so have the phenomena of evening and morning, is easy to apprehend. The fact is certain; the "how" was no difficulty to Him Who spoke and it was done. Our place is to honour Him in believing His word, without which faith nothing is as it should be. Another first day was to behold a better light; there, too, still more conspicuously, if that True Light shone when all was profounder darkness, He too had been before the darkness.

It is remarkable in this passage that God saw the light, and recognizing its goodness, brought in division between light and darkness.

No doubt whilst this stands as a great physical fact in nature marked by the beneficence of an all-wise Creator, it is intended to symbolize the great division between moral light and moral darkness. This principle runs all through Scripture. It is exemplified to the full in Him, who was the Light of the world.

"And God saw the light, that it was good" - and divided it from darkness - separated the two - first darkness on the earth, then light

Again we have the words, "and God saw that it was good." That creation should be under authority and control was good. We find, alas! that man, when created as the head of things, soon repudiated the Divine authority and plunged into lawlessness, which is sin. That emphatically is not good, but it should make every believer keenly realize how important it is to be subject in all things to the authority of the word of God.

Then again, they were to rule the day and the night respectively. From the outset the earth was placed under the rule and control of heaven, even as regards the action of inanimate matter, so that in this these heavenly bodies become a sign that "the heavens do rule" (Dan. 4:26), and a faint prophecy of "the kingdom of heaven," of which we read in the Gospel of Matthew. The sad fact confronts us that fallen man soon perverted all this, and began to worship these lights as though they were creator and not creature, thereby changing God's truth into a lie. Romans 1:25 refers to this, we believe.

The fifth division of mere creation, and an ordered kosmos adorned, and peopled with moving life, ends with the earth bringing forth living creatures; God closes it by "God saw that it was good."

Here experience is necessarily at fault. For only the Bible could give us the truth as to the primitive phase of man and the creatures around him. But it at once approves itself, when revealed, as being the sole conceivable state in which the Creator could have placed creation and its head suitably to His own goodness. Hence the force and moral beauty of His final survey in the last verse. "And God saw everything that he had made (i.e., in the Adamic earth), and behold, it was very good." So with the one exception of day second had He called each thing "good"; now as a whole it was superlatively so in His eyes.

No wonder that God as He viewed with deep complacency the work of His hands, proclaimed it as VERY GOOD.