Tafsir Ibn Kathir
© Dar us Salam
And We have appointed the night and the day as two Ayat (signs). Then, We have obliterated the sign of the night (with darkness) while We have made the sign of the day illuminating, that you may seek bounty from your Lord, and that you may know the number of the years and to count (periods of time). And We have explained everything in detail with full explanation.
[Surah Al-Isra 17 Ayah 12]
Allah reminds us of the great signs that He created, including the alternation of the night and day, so that people may rest at night, and go out and earn a living, do their work, and travel during the day, and so that they may know the number of days, weeks, months and years, so they will know the appointed times for paying debts, doing acts of worship, dealing with transactions, paying rents and so on. Allah says:
that you may seek bounty from your Lord.
meaning in your living and travels etc.
and that you may know the number of years and to count.
If time stood still and never changed, we would not know any of these things, as Allah says:
Say: “Tell me! If Allah made the night continuous for you till the Day of resurrection, which god besides Allah could bring you light? Will you not then hear?” Say: 'Tell me! If Allah made the day continuous for you till the Day of resurrection, which god besides Allah could bring you night wherein you rest? Will you not then see? It is out of His mercy that He has made for you the night and the day that you may rest therein and that you may seek of His bounty - and in order that you may be grateful.
[Surah Al-Qasas 28 Ayahs 71-73]
Blessed be He Who has placed the big stars in the heaven, and has placed therein a great lamp (sun), and a moon giving light. And He it is Who has put the night and the day in succession, for such who desires to remember or desires to show his gratitude.
[Surah Al-Furqan 25 Ayahs 61-62]
and His is the alternation of the night and day
[Surah Al-Mu’minun 23 Ayah 80]
He makes the night to go in the day and makes the day to go in the night. and He has subjected the sun and the moon (to His law). Each running (on a fixed course) for an appointed term. Is not He the Exalted in Power - He Who forgives again and again?
[Surah Az-Zumar 39 Ayah 5]
(He is the) Cleaver of the daybreak. He has appointed the night for resting, and the sun and the moon for reckoning. Such is the measuring of the All-Mighty, the All-Knowing.
[Surah Al-An’am 6 Ayah 96]
And a sign for them is the night. We withdraw therefrom the day, and behold, they are in darkness. And the sun runs on its fixed course for a term (appointed). That is the decree of the All-Mighty, the All-Knowing.
[Surah Ya-Sin 36 Ayah 37-38]
Allah has made the night a sign having distinguishing features by which it is known. These features include the darkness and the appearance of the moon. The day also has distinguishing features by which it is known; the light and the appearance of the shining sun. He has made a distinction between the light of the moon and the light of the sun so that they may be distinguished from one another, as Allah says:
It is He Who made the sun a shining thing and the moon a light and measured for it stages that you might know the number of years and to count (periods of time). Allah did not create this but in truth.
[Surah Yunus 10 Ayah 5 ]
Verily, in the alternation of the night and the day, and in all that Allah hath created, in the heavens and the earth, are signs for those who fear Him.
[Surah Yunus 10 Ayah 6]
They ask you about the crescent moons. Say: “These are signs to mark fixed periods of time for mankind and for the pilgramage.”
[Surah Al-Baqarah 2 Ayah 189]
Then, We have obliterated the sign of the night with darkness while We have made the sign of the day ilumminating,
Ibn Jurayj reported that 'Abdullah bin Kathir commented on this Ayah: “[It means] the darkness of the night and the twilight of the day.”
[At Tabari 17:396]
Ibn Jurayj reported that Mujahid said: "the sun is the sign of the day and moon is the sign of the night.
We have obliterated the sign of the night
this refers to the moon’s blackness, which is how Allah has created it."
[At Tabari 17:396]
And We have appointed the night and the days as two Ayat (signs).
Ibn Abi Najih reported that Ibn 'Abbas said: “By night and day, this is how Allah created them, may He be glorified.”
[At Tabari 17:397]
http://www.quraan.com/Tafsir/TheNightAndDay.asp
“I put my trust in Allah, my Lord and your Lord! There is not a moving creature, but He has a grasp of its forelock. Verily, my Lord is on the straight path. (The truth)”
(11:55-56)
“…Indeed my prayer, my sacrifice, my living and my dying are for Allaah, the Lord of the worlds” (6:162)