Surah Al-Qasas, Ayah 71

Say - O Messenger, to these idolaters: Tell me if Allah were to make the light last continuously for you, without any break until the Day of Judgment, which god besides Allah can bring you light like that of day? Do you not hear these proofs and know that there is no god besides Allah who can bring that to you?

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? (71)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? (72)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 (73)

Night and Day are among the Blessings of Allah and are Signs of Tawhid

Allah reminds His servants of His favors towards them by subjugating for them the night and day, without which they could not survive. He explains that if He made the night continuous, lasting until the Day of Resurrection, that would be harmful for them and would cause boredom and stress. So He says:

مَنْ إِلَٰهٌ غَيْرُ اللَّهِ يَأْتِيكُمْ بِضِيَاءٍ

(which god besides Allah could bring you light?) meaning, 'with which you could see things and which would bring you relief?'

أَفَلَا تَسْمَعُونَ

(Will you not then hear?) Then Allah tells us that if He had made the day continuous, lasting until the Day of Resurrection, that would also be harmful for them and their bodies would get tired from so much movement and activity. Allah says:

مَنْ إِلَٰهٌ غَيْرُ اللَّهِ يَأْتِيكُمْ بِلَيْلٍ تَسْكُنُونَ فِيهِ ۖ

(which god besides Allah could bring you night wherein you rest?) meaning, 'to rest from your work and activity.'

أَفَلَا تُبْصِرُونَ - وَمِنْ رَحْمَتِهِ

(Will you not then see? It is out of His mercy) towards you,

جَعَلَ لَكُمُ اللَّيْلَ وَالنَّهَارَ

(that He has made for you the night and the day) He created both,

لِتَسْكُنُوا فِيهِ

(that you may rest therein) during the night,

وَلِتَبْتَغُوا مِنْ فَضْلِهِ

(and that you may seek of His bounty) during the day, by traveling, moving about and working.

وَلَعَلَّكُمْ تَشْكُرُونَ

(and in order that you may be grateful.) So that you may give thanks to Allah by performing all kinds of acts of worship at night and during the day. Whoever misses something during the night can make it up during the day, and vice versa. This is like the Ayah,

وَهُوَ الَّذِي جَعَلَ اللَّيْلَ وَالنَّهَارَ خِلْفَةً لِمَنْ أَرَادَ أَنْ يَذَّكَّرَ أَوْ أَرَادَ شُكُورًا

(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.)(25:62). And there are many similar Ayat.