Tafsir of An-Naba' 78:39

That is the True Day.

"That" is a demonstrative referring to the day of their standing [before Allah] in the manner previously described. The use of the distant demonstrative, despite the proximity of the reference, is to signal its high status and exalted position in terms of terror and grandeur. Its grammatical position is nominative as the subject (mubtada'), and its predicate is the word "the Day" (al-yawm), which is described by the words of the Exalted, "the True." Alternatively, "the Day" could be a substitute (badal) or an explanatory appositive (‘atf bayan). The meaning of "the True" is that which is established and certain; meaning, that day is established and will come to pass without fail. This sentence acts as a confirmation of what preceded it, which is why it is not connected by a conjunction.

The "fa" (so) in His saying, the Mighty and Majestic, "So whoever wills may take to his Lord a way of return," is an eloquent "fa" (fa' fasihah) that reveals a deleted conditional clause. The object of the verb "wills" is also deleted, indicated by the reward that follows. "To His Lord" is placed before the verb to emphasize it and to observe the rhythmic endings of the verses. It is as if it were said: "Since the matter is as described—that the aforementioned event is certain to occur without fail—whoever wills to take a path of return to the reward of his Lord, whose magnificent status has been mentioned, let him do so through faith and obedience."

Qatadah said, in a narration from ‘Abd ibn Humayd, ‘Abd al-Razzaq, and Ibn al-Mundhir, that "a way of return" (ma'aban) means a path. The prepositional phrase relates to it because it contains the meaning of reaching or arriving. The first interpretation is more evident. It is said that adding a missing noun (i.e., "the reward") is necessary because it is impossible to return to His Divine Essence, the Mighty and Majestic. It is also said that it is because the return of every person to their Lord, the Glorified, is not a matter of their own will, as it is inevitable whether they want it or not. Thus, what is linked to the will is the return to His reward, for the servant has the choice regarding faith and obedience, and there is no reward without them. It is also argued that this is due to the preceding verse, "for the transgressors a place of return," as they also have a return to Allah, the Exalted, but it is for punishment, not for reward; and for everyone is a direction toward which they face.