Like the previous Surahs, Allah (swt) swears by night and daytime, both of them are the greatest visible signs that no one can deny, like the sun and the moon. Allah (swt) made the night calm, attire, rest and serenity, and made the daytime for action and activity. Activity during the day cannot be achieved unless there is rest at night, that is why they are integrated, not conflicting; each of them has a function. Allah (swt) mentions the night first then the day because you cannot act properly during the day unless the function of night is executed properly, this is of Allah’s mercy:

 {وَمِن رَّحْمَتِهِ جَعَلَ لَكُمُ اللَّيْلَ وَالنَّهَارَ لِتَسْكُنُوا فِيهِ وَلِتَبْتَغُوا مِن فَضْلِهِ وَلَعَلَّكُمْ تَشْكُرُونَ }

(And out of His mercy He made for you the night and the day that you may rest therein and [by day] seek from His bounty and [that] perhaps you will be grateful.) (Al-Qassas: 73)