وَالنَّهارِ إِذا جَلّاها

By the day when it reveals her.

EXEGESIS

Jallāhā (reveals her) is combined of the verb jallā, the subject of which is the day, and the pronoun hā (her) which refers to the sun as an object. Thus the meaning is: I swear by the day when it reveals the sun.

However, if we take the pronoun to refer to the earth, as do several exegetes,^{‎[1]Mizan, 20/296; Mudarrisi, 18/134.} which is implicitly understood based on the context, the meaning would be: I swear by the day when it reveals the earth for people to see. In other words, the surah is swearing by the day when it reveals the earth through its daylight.^{‎[2]Munyah, 30/378.}

EXPOSITION

The oath by the day when it reveals the sun may seem somewhat odd, for it seems that it is the sun that reveals the day and not vice versa. Perhaps one way of understanding this is to look at how the earth rotates around the sun, in which part of the earth faces the sun while another part is in darkness. When half of the earth is facing the sun it would be correct to say the day is revealing the sun, similar to how we intellectually traverse from an effect to its cause. It is during the daytime that we can observe the sun. Accordingly, it would be correct to say the day reveals the sun.

REVIEW OF TAFSĪR LITERATURE

Some other weak opinions regarding the pronoun her are that it refers to the world, or to darkness,^{‎[3]Tabrisi, 10/755.} or that the subject of the verb reveals is God and the object is the sun, and thus the meaning would be: I swear by the day when Allah reveals the sun.^{‎[4]Mizan, 20/296.}

[1] Mizan, 20/296; Mudarrisi, 18/134.
[2] Munyah, 30/378.
[3] Tabrisi, 10/755.
[4] Mizan, 20/296.