Genèse 1:14

"Let there be luminaries:" They were created from the first day; and on the fourth day, He commanded them to be suspended in the heavens. And so [too], all of the issue of the heavens and the earth were created from the first day, and each one was affixed on the day that was decreed about it. That is why it is written (verse 1), "et (a Hebrew preposition, which can either proceed a direct object or mean 'with,' and so, is often seen as indicating additional meaning) hashamayim (the heavens)," in order to include their issue,”and "et haarets (the earth)," in order to include its issue.

"Let there be luminaries:" Luminaries (meorot) is written [in its incomplete spelling] lacking the [letter,] vav. [It can thus also be read as the word, curses (ma'arot)], since it is the day of the curse that babies get sick with croup. And that is what we learned (Sofrim 17:5), “on the fourth day [Wednesdays], they would fast so that the babies would not get sick with croup.”

"To separate between the day and the night:" [This happened] after the first light was hidden away, but during the seven days of Creation, the first light and the first darkness served - whether by day or whether by night.

"And they will be for signs:" When the luminaries are eclipsed, it is a bad sign for the world, as it is stated (Jeremiah 10:2), "from the signs of the sky do not fear;" [meaning that only] when you do the will of the Holy One, blessed be He, do you not need to fear from calamity.

"And for appointed times:" [It was stated] based on the future, since in the future, Israel would be commanded regarding the festivals; and those would be [determined based] on the appearance of the [new] moon.

"And for days:" The service of the sun is half a day and the service of the moon is [for the duration] of its [other] half; behold that is a full day.

"And for years:" At the end of 365 days, they complete their orbit through the twelve constellations that serve them - and that is a year. (And they go back and begin to rotate around the circuit like their first trajectories a second time.)

And the Lord said, Let there be lights in the expanse of the heavens, to distinguish between the day and the night; and let them be for signs and for festival times, and for the numbering by them the account of days, and for the sanctifying of the beginning of months, and the beginning of years, the passing away of months, and the passing away of years, the revolutions of the sun, the birth of the moon, and the revolvings (of seasons).

"And He said" - The word yehi is [identical to] yihyeh ("let there be/there will be"). And since it is used frequently, it is [the same form] for singular and plural, also for feminine: "if there will be (yehi) a young virgin woman..." Deuteronomy 22:23

"for signs" - moments "and for appointed times" - hours. It's also possible that "signs" refers to the lunar and solar eclipses and {PRESENTLY INCOMPLETE}

"and they shall be for signs" - A great Spanish sage said that the firmament is divided into eight parts, for the seven planets and the sphere of constellations, but this cannot be, for there is no physical body above the sphere of the constellations. Now behold, the text says, "in the firmaments of the heavens", which indicates that there is a heaven beyond the firmament. And likewise, "the heavens of the heavens", "for the one who rides in the heavens of the heavens of yore" kedem - where kedem here does not signify "east". Now the gaon Rav Sa'adia (may the memory of a righteous individual be for blessing), fled from this place [i.e., did not expound this]. What is correct in my eyes: The sun and the moon and all the stars/planets are luminaries in the firmament, for there they appear [to us to be]

LET THERE BE LIGHTS. Now the light was created on the first day, illuminating the elements, but when on the second day the firmament was made, it intercepted the light and prevented it from illuminating the lower elements. Thus, when the earth was created on the third day there was darkness on it and not light. And now on the fourth day the Holy One, blessed be He, desired that there be in the firmament luminaries, the light of which would reach the earth. This is the meaning of the words, in the firmament of the heaven to give light upon the earth, for there already was light above the firmament which did not illuminate the earth.
The meaning of the words, Let there be lights, is as follows: He decreed on the first day that from the substance of the heavens there should come forth a light for the period of the day, and now He decreed that it become corporeal and that a luminous body come forth from it which would give light during the day with a great illumination, and that another body of lesser light [should come into existence] to illumine at night, and He suspended both in the firmament of the heavens in order that they illumine below as well.
It is possible that just as He endowed the earth with the power of growth in certain places thereof, so He placed in the firmament certain areas that are prepared and ready to receive the light, and these bodies which receive the light reflect it, just as window-panes and onyx stones. This is why He called them me’oroth and not orim. [Orim would imply that they have their own light; me’oroth on the other hand implies that they reflect the light which they receive], even though they are called orim, in the Psalm..

יהי מארות, “let there be luminaries;” it is common for the Torah to apply a singular mode to nouns described in the plural, such as in Numbers 9,6 ויהי אנשים אשר היו טמאים, “there was (singular) men who were ritually impure, etc." The meaning of our verse here is: “let a certain process occur as a result of which luminaries will materialise in the sky of the heavens.”

ברקיע השמים, in the firmament which spans the heavens.

ברקיע, seeing that the word ברקיע is in the construct mode, linked to the word following it, i.e. “the sky of the heaven, the ra-kia, the vowel under the letter ר is a brief one, chataf, such as the difference between katzir, harvest, and k’tzir chittim, “wheat harvest,” where the word k’tzir is in the construct mode, belonging to the word chittim, wheat. (Ruth 2,23) להבדיל בין היום ובין הלילה, the Torah had already mentioned earlier (verse 4) that G’d had made a separation between light and dark, so what need was there for the luminaries in order to accomplish this? The fact is that up until this point the precise point when night or day commences and ends had not yet been defined. This came about only when the sunrise and sunset became visible observable phenomena on earth. Similarly, the advent of visible stars in the sky now signaled that dusk had come to an end. להבדיל בין (תחלת) היום ובין (תחלת) הלילה, to separate night from the beginning of the day and day from the beginning of the night.

והיו לאותות ולמועדים, an oblique reference to Kings II 20,8-9 where King Chizkiyah had asked G’d for a sign in the sky that Isaiah’s promise that the decree of his death had been cancelled and that G’d had added another 15 years to his life was definitive. We have other verses (Yoel 3,3) as well as Jeremiah 10,2 in which these phenomena in the sky are described as clear signals by G’d to man of things to come.

ולמועדים, the orbit of the moon which renews its path every 29 and a half days serves as a legal instrument used in determining dates which appear in documents used by the Jewish people. Compare what David wrote about this in Psalms 104,19

ולימים, and as days. Upon investigation it will be seen that certain stars orbit at intervals of exactly 24 hours.

ושנים, and as years, a reference to the four seasons of the year, which together comprise an entire year.

יהי מאורות ברקיע השמים, the planets created on the second day should now begin to function by providing light. Their influence should be concentrated on the “lower” universe, as it is visible to us with our senses. Everything mentioned in this paragraph refers to sensations perceived by the creatures on earth. By traversing pure waters on the way to earth, the light refracted by these luminaries is increased manifold.

ויאמר אלוקים יהי מארות ברקיע השמים, we do not find many occasions when the verb היה occurs within strictly defined grammatical parameters in accordance with the rules applying to differentiating between singular and plural, or the rules applying to distinguishing between masculine and feminine subjects. As a result, the Torah here writes יהי in the singular mode, although G’d gave a directive involving a whole multitude of new phenomena that were to appear in the sky. Compare also Deut 22,23 כי יהיה נערה בתולה, where the Torah employs the masculine pronoun when referring to a young girl, still a virgin.
These luminaries were created during the first “day” together with the planets (fixed stars) as we explained on verse 3; however, their light was not transmitted to earth seeing there had not been an atmosphere at yet. [our astronauts only discovered that there is utter darkness beyond the stratosphere when they took the first space flight beyond these regions. Ed.] Besides, the earth was not yet sufficiently dry. Once it had dried sufficiently, in accordance with G’d’s will, it commenced complying with G’d’s directive on the morning of the third “day” to produce herbs, etc. By the fourth “day” it had become much stronger, firmer, so that when G’d gave a directive to the luminaries, these were able to respond in accordance with G’d’s directive. As a result the plants produced by the earth would contain seeds, the trees would bear fruit, etc. This is the meaning of the statement by our sages in Rosh Hashanah 11 that the entire work of creation was created in their full potential, fully mature, i.e. on the fourth day the vegetation, including herbs and trees had attained its full growth. All the creatures created subsequently also were created in their full size, maturity, as appropriate to each separate species. When the Talmud there adds the words בדעתן בצביונן נבראו, this means that the creatures equipped with intelligence possessed it from the moment they were created, whereas those not meant to possess intelligence would not develop it at a later stage either. Man was able to recognise the nature and essence of each creature as well as its function in the universe. This is what Solomon had in mind when he said in Kohelet 3,11 את הכל עשה יפה בעתו, “He brought everything to pass precisely at its time.”
The reason the herbs, etc. attained their ultimate size, etc. on the fourth “day,” was because they required the input of the celestial bodies for this, something that had not been present on the third “day.” This is what the sages (Chagigah 12) referred to when they said הן הן המאורות שנבראו ביום ראשון אלא שלא תלאן עד יום רביעי, “these (the ones mentioned on the fourth ‘day’) are the ones which had been created on the first ‘day,’ but He had not placed them in orbit until the fourth ‘day.’” The word תלה means to hang something from the top down. ברקיע השמים, the atmosphere; this is also the meaning of the word when we read על פני רקיע השמים. (verse 20) This region is called רקיע, because, as we explained on verse 8, it is something stretched taut over a large expanse of space. G’d attached it to the heaven, i.e. to the various planets, seeing that it is secondary in importance to them, receiving its light from them.