Allah tells us about the signs He created that are indicative of His complete power and great might. He made the rays that come forth from the bright sun as the source of light, and made the beams that come forth from the moon as light. He made them of two different natures so they would not be confused with one another. Allah made the dominion of the sun in the daytime and the moon in the night. He ordained phases for the moon, where it starts small then its light increases until it completes a full moon. Then it begins to decrease until it returns to its first phase at the conclusion of the month. Allah said:

(And the moon, We have measured for it mansions (to traverse) till it returns like the old dried curved date stalk. It is not for the sun to overtake the moon, nor does the night outstrip the day. They all float, each in an orbit.) (36:39-40)

And He said:

(And the sun and the moon for counting) [6:96] And in this Ayah He said:

(and measured) that is the moon, Allah said:

(And measured out for it stages that you might know the number of years and the reckoning.")

The days are revealed by the action of the sun, and the months and the years by the moon. Allah then stated

(Allah did not create this but in truth.)

He didn't create that for amusement but with great wisdom and perfect reasoning. With a similar meaning, Allah said:

(And We created not the heaven and the earth and all that is between them without purpose! That is the consideration of those who disbelieve! Then woe to those who disbelieve from the Fire!) (38:27) He also said:

("Did you think that We had created you in play (without any purpose), and that you would not be brought back to Us?" So Exalted be Allah, the True King: None has the right to be worshipped but He, the Lord of the Supreme Throne!) [23:115-116]

Allah said:

(He explains the Ayat in detail for people who have knowledge.) In other words, He explained the signs and proofs for people who know.

Allah further stated:

(Verily, in the alternation of the night and the day)

The day and the night alternate, when one arrives, the other goes, and so on, with no errors. This is similar to the meaning indicated in the following Ayat:

(He brings the night as a cover over the day, seeking it rapidly...).

(It is not for the sun to overtake the moon.) [36:40], and

((He is the) Cleaver of the daybreak. He has appointed the night for resting). [6:96]

Allah continued:

(and in all that Allah has created in the heavens and the earth) meaning the signs that indicate His greatness. This is similar to Allah's statements:

(And how many a sign in the heavens and the earth...) [12:105],

("Say: "Behold all that is in the heavens and the earth," but neither Ayat nor warners benefit those who believe not.) [10:101]

(See they not what is before them and what is behind them, of the heaven and the earth.) [34:9].

(Verily, in the creation of the heavens and the earth, and in the alternation of night and day, there are indeed signs for men of understanding.) [3:190] means intelligent men. Allah said here,

(Āyāt for those who have Taqwa.) meaning fear Allah's punishment, wrath and torment.