They will make excuses to you when...
"They will make excuses to you"—This is an explanation of what they resort to upon your return to them. It is said that the address is to the Prophet (peace be upon him), and the plural is for glorification. It is more appropriate that it refers to him (peace be upon him) and his companions, for they used to offer excuses to everyone; meaning, they offer excuses to you for remaining behind.
"When you return"—from the expedition, arriving to them. The reason He (subhanahu) did not say "to Medina" is to signal that the pivot of the excuse is the return to them, not the return to the city; for perhaps some of them rushed to offer excuses before [the Prophet] returned to it. The address is directed to him (peace be upon him), and it is specified as such because the response is his (peace be upon him) duty.
"Do not make excuses"—meaning, do not perform the act of excusing, or do not offer the excuses you possess.
"We will not believe you"—This is a commencement to explain the cause of the prohibition. His saying "and His Messenger"—the object of the verb "to see" is placed before the subject to signal the difference in the state of the two visions and their disparity, and to intimate that the pivot of the threat is upon Him (Azza wa Jall) regarding their deeds.
"Then you will be returned"—on the Day of Resurrection—"to the Knower of the unseen and the witnessed"—for requital according to what appeared of your deeds. The description is placed in the position of the pronoun to intensify the threat; for He (subhanahu) knows all their deeds, manifest and hidden, and His encompassing of their circumstances, prominent and latent, necessitates a great deterrent. Regarding the precedence of "the unseen" over "the witnessed," it is said: to establish that the proportion of His (ta’ala) encompassing knowledge to all things, secret or public, is one and the same, in the most eloquent and emphatic manner. How could it be otherwise, when His (ta’ala) knowledge of His objects of knowledge is exalted above being by way of obtaining an image? Rather, the existence of every thing and its realization in itself is knowledge in relation to Him (ta’ala), and in this sense, the state does not differ between matters that are prominent and those that are latent.
It is not hidden from you that this is an assertion that His (subhanahu) knowledge of things is "presential" (huduri) and not "acquired" (husuli). This has been objected to based on the inclusion of His (Jalla wa ‘Ala) knowledge of the impossible and the non-existent possibilities, whereas presential knowledge is restricted to existing entities, because it is the presence of the known thing in its objective form before the knower. Thus, how could the state not differ between prominent and latent matters, given that the latent includes non-existent possibilities and impossibilities, in which realization in themselves cannot be conceived so as to be knowledge for Him (ta’ala)? This is what has been said, and there is a view on it. The verification of the Necessary Being's (subhanahu) knowledge of things is among the difficult discussions and thorny issues in which the understandings of many have been bewildered and the feet of eminent scholars have stumbled. Perhaps the turn will come, if Allah (ta’ala) wills, to verify this.
"Then He will inform you"—at the time of your return to Him (subhanahu) and your standing before Him—"of what you used to do"—meaning, of the deeds you performed continuously in the world, the past and the subsequent, provided that "what" (ma) is relative; or [He will inform you] of your continuous deeds, provided that "what" (ma) is infinitive. The intent behind "informing" in this context is requital for them. The preference for this term over "punishment" is to observe what preceded of His (ta’ala) saying: "Allah has already informed us..." and so on, and to intimate that they were not aware in the world of the true reality of their deeds, and that they shall only know them on that Day.