Commentary for Genesis 1:18

ולהבדיל בין האור ובין החושך, between the period when light begins and the period when darkness begins. Sunrise is the period when light begins, whereas the clear visibility of the stars in the evening is the period when the darkness begins.

ולמשול ביום ובלילה, in order to bring new creatures into life in the “lower” regions of the universe, i.e. these living creatures, as opposed to the plants, required more than the light G’d had created on the first day. Seeing they are more important and more sophisticated beings they require exposure to better light in order to flourish.

And to rule over the day and the night (velimshol bayom ouvalila): The root, mem-shin-lamed (to rule) is connected to the [letter,] bet [after it], as [is the case with] (Genesis 37:8), "will you surely rule over us (timshol banu)." And the intention is that the night and the day be under the rulership of the luminaries as I have explained; and not that they will rule over the lower beings, this one by day and this one by night as is the opinion of Ramban. And this matter still requires much study, and maybe [Ramban] is right; and so did the Psalmist say (Psalms 136:8-9), "for the government of the day... for the government of the night." And it appears that this is what the author of the cantillation marks intended in verse 16, as he wanted to attach "and the small luminary to rule the night" with "and the stars;" as the psalmist [there] said, "and the moon and the stars for the government of the night."

And to separate between the light and the darkness: By this, the verse adds that besides their coming to separate between the day and the night, they also came to separate between the light and the darkness. Since, in truth, even if the luminaries were equal in their light, nonetheless, they would still be different in their appearance; and day would be divided and distinguishable from night. But rather, they also came to separate between the light and the darkness; since the light of the sun is so strong, that even on a cloudy day [when] the light of the sun is [altogether] covered with clouds, nonetheless the day is light - 'and on a cloudy day, it is all sunny.' Which is not the case with the light of the moon - if the clouds cover the light, behold it becomes dark. And all of this is with regards to the light of the luminaries, but on the first three days, within which the first light was in use, the same separation that came between the night and the day separated between the light and the darkness; that in the absence of light came the night and darkness together.

AND TO RULE OVER THE DAY AND OVER THE NIGHT. The matter of rulership is a different matter from the function of light which He mentioned, since it includes that which He stated at first, And they shall be for signs, and seasons. Their rulership over the earth comprises the changes which they cause in it and the power of bringing about the existence and deterioration of all things in the lower world since the sun, by its rule during the day, causes the sprouting, the propagation and the growth of all the warm and dry things, while the moon by its rule increases the springs and the oceans, and all liquid and cold things. Therefore He said in a general way, And to rule over the day and over the night, because theirs is the dominion over things in the lower world.
It is possible that the rulership given to them contains also a power of emanation for they are the leaders of things in the lower world, and with their power, every ruling power in nature holds sway. Thus the constellation which comes up by day rules during it, even as it is written, The sun and the moon and the stars… which the Eternal thy G-d hath allotted unto all the peoples.¹⁶⁰Deuteronomy 4:19. And this is what Scripture means when it says, He counteth the number of the stars; He giveth them all their names,¹⁶¹Psalms 147:4. likewise, He calleth them all by name.¹⁶²Isaiah 40:26. For the calling of names signifies the differentiation in their respective powers, giving to this one the power of justice and righteousness, and to that one the power of blood and the sword, and similarly all other powers, as is known in astrology. And all is done by the power of the Most High and in accordance with His Will. Therefore it says, Great is our Lord, and mighty in power,¹⁶³Psalms 147:5. for He is greatest of all and mightiest in power over them. And similarly it says, He calleth them all by name by the greatness of His might and the strength of His power.¹⁶²Isaiah 40:26. In accord with the secret I have hinted to you, the matter of rulership is completely true.

ולמשול ביום ובלילה, the one, i.e. the sun by day, and the other, i.e. the moon, to govern by night.

ולמשול ביום ובלילה, “and to have dominion by day and night respectively.” This “dominion” would manifest itself in these luminaries materially influencing changes on earth, such as in the growth of vegetation, climate changes at different times of the year, etc. The sun would govern matters involving heat and dryness, whereas the moon would govern matters involving cold and wet matters (high and low tide of the oceans, as well as the promoting of plant growth in the watery regions.)

ולמשול ביום ובלילה, “and to rule during the day and the night.” One would rule by day, the other by night. The moon even when visible by day, hardly “rules.” Or, in the words of the moon itself, quoted in the Talmud Chulin folio 60, “who needs light at noontime?”

ולהבדיל בין האור ובין החושך, to establish clear demarcations amongst the inhabitants of the lower regions of the universe, between when these respective luminaries were to shine, and when they were to set, i.e. to disappear from view. Basically, the meaning is the same as in verse 14 above.

And to separate between the light and the darkness: That the light and the darkness should be set and separated in their times.

ולהבדיל, from the time the sun rises it is light, day, and the domain of the sun, whereas from the time the stars become visible in the sky, it is nighttime, the moon’s domain. The night is called “darkness,” even though there is some light in the sky illuminating parts of the earth in a fashion.

ולהבדיל בין האור והחושך, ”as well as to separate daylight from darkness.” According to Ibn Ezra, the function of separating between daylight and darkness is one performed by both the sun and the moon. Both sun and moon at daybreak and in the evening, signal by their appearance that the darkness or daylight respectively is about to emerge or disappear. Nachmanides understands the words אור and חושך as alternates for “day” and “night.” as this is the name give to light and darkness respectively. We have been told this already in verse 7, when G’d named these phenomena accordingly, having in mind more advanced stages of the development of the universe. Our verse would simply mean that the sun governs by day whereas the moon governs by night.

AND TO DIVIDE THE LIGHT FROM THE DARKNESS. Rabbi Abraham ibn Ezra said: “By the coming forth of the sun at daytime and the light of the moon at night, they shall divide the light from the darkness.”¹⁶⁴Ibn Ezra’s opinion is that the word ul’havdil (and to divide) refers to both the sun and moon, that each in coming forth separates between light and darkness. (Tur.) In my opinion, the light mentioned here refers to the day, and the darkness is the night for such are their names, as it says, And G-d called the light Day, and the darkness He called Night.¹⁶⁵Verse 5. Thus according to Ramban, the meaning of the verse is: “and to divide the day from the night,” meaning, that light is to serve at daytime and darkness at night. (Tur.)
Now in connection with all the works of creation, Scripture mentions the Divine command and then tells of the deed. And here too He commanded, And they shall be for lights,¹⁶⁶Verse 15. and then it relates, And G-d set them.¹⁶⁷Verse 17. He further said, And to rule over the day and over the night,¹⁶⁸Verse 18. meaning that one is to rule by day and the other by night, the rulership being that which He commanded when He said, And they shall be for signs, and for seasons.¹⁶⁹Verse 14. And now He related that the rulership of the two is not alike but instead consists of dividing the darkness from the light. The greater luminary will rule by day and light will be everywhere, even where the sun does not reach, and the smaller luminary will rule by night, and there will be darkness except that the moon will lighten its darkness. This then is the command He gave in order to divide the day from the night,¹⁶⁹Verse 14. as it says, And G-d divided the light from the darkness.¹⁵³Verse 4.

ולהבדיל בין האור ובין החשך, “and in order to make a clear separation between periods of light and periods of darkness.” This phrase does not refer to either the sun or the moon. The Torah had already told us in verse 14 that this would be the function of the great luminaries. The phrase therefore refers to the stars, whose visibility tells us if it is day or night. They become visible when day fades, and they fade when dawn approaches.

וירא אלוקים את האור כי טוב, “G’d saw the light that it was good.” The belief that the system of luminaries was beneficial for the creatures on earth is based on the availability of light and darkness. We read in Job 9,9 עושה עש כסיל וכימה וחדרי תימן, “the One who makes the Bear and the Orion, Pleiades and the chambers of the south wind.” The constellation Pleiades supposedly cools, whereas the constellation Orion supposedly causes warmth on earth. The constellations each fulfil opposite roles and are matched one against the other. Each of them helps the growth and ripening of a variety of plants and fruit in its own fashion. This is also what G’d had in mind in Job 38,31 when He had asked Job: “can you tie cords to Pleiades?” People on earth obtain an insight into G’d’s power by observing the operation of the forces of nature and marveling at the intelligence which created such a system. As a result of their appreciation of G’d’s intelligence and power they praise Him. This is what Isaiah 40,26 spoke of when he urged the people שאו מרום עיניכם וראו מי ברא אלה, “raise up your eyes to the heavens and behold who has created all these?” All of this is meant when our verse reports that G’d took a look at how His directive had been carried out and concluded that the results were good.
Another reason G’d referred to all this as טוב, ”good,” is that He foresaw already the great miracle which would be invoked in the future when Joshua would bid the sun and the moon to stop orbiting until he had completed his pursuit of the Canaanites (Joshua 10,12). The wording there is שמש בגבעון דום וירח בעמק אילון, “stand still sun at Gibeon and moon in the valley of Ayalon.” Another reference to a similar miracle is found in Judges 5,20 where the prophetess Devorah describes the stars as having changed their orbit to help Barak fight Siserah.