Tafsir of At-Taghabun 64:9

[Linguistic Readings] It is recited as najma‘ukum (We gather you), nukaffir (We shall expiate), and nudkhilhu (We shall admit him), in both the yā’ (third-person) and nūn (first-person plural) forms.

[Grammatical Analysis] If you ask: What governs the accusative case of the adverbial phrase (yawma - the Day)? I say: It is governed by His saying: "He will inform you" (la-tunabbi’unna), or by "All-Aware" (khabīr), due to the sense of warning contained within it—as if it were said: "And Allah will punish you on the Day He gathers you." Or, it is governed by an implied "Remember" (udhkur).

[Exegesis of "The Day of Gathering"] "For the Day of Gathering" (li-yawm al-jam‘): The Day on which the first and the last are gathered.

[Exegesis of "At-Taghābun"] "At-Taghābun" (The Day of Mutual Disillusion/Loss): A metaphor derived from people cheating one another in trade, where one party gains at the expense of the other. This is because the fortunate will occupy the stations of the wretched—which the wretched would have occupied had they been fortunate—and the wretched will occupy the stations of the fortunate—which the fortunate would have occupied had they been wretched. It contains a mockery of the wretched, for their descent is not a true "cheating" (as they have no claim to those stations).

[The Hadith] In the Hadith of the Messenger of Allah (ﷺ): "There is no servant who enters Paradise but that he is shown his seat in the Fire, had he done evil, so that he may increase in gratitude. And there is no servant who enters the Fire but that he is shown his seat in Paradise, had he done good, so that he may increase in regret."

[Conclusion on the Term] The meaning of "That is the Day of Mutual Loss" is an exaltation of that Day, implying that its loss is the true loss, not the losses in worldly affairs, however great or significant they may be.

[Grammatical Note] "Righteous" (ṣāliḥan) is an adjective for an implied verbal noun, meaning: a righteous deed (‘amalan ṣāliḥan).