Tafsir of Al-Isra 17:45

(And when you recite the Qur’an) — which speaks of glorification, sanctification, and calling them to act upon what is within it — (We place) by Our power and Our will, which is established upon hidden wisdom, (between you and those who do not believe in the Hereafter) — who are the polytheists previously mentioned. The relative pronoun [Al-ladhina] was preferred over a pronoun [such as 'them'] to disparage them through the content of the relative clause, and to complete the indication of their disbelief in both the Origin and the Return, alongside what preceded.

It is stated in Irshad al-'Aql al-Salim that disbelief in the Hereafter was specifically mentioned among all the things they disbelieved in—such as Monotheism and the like—as an indication that it is the most significant matter they were commanded to believe in within the Qur’an, and as a preparation for the denial of resurrection, the demand for its hastening, and similar things that will be narrated from them. Regarding the claim that the Hereafter is the most significant matter they were commanded to believe in, some have wavered, as it might be argued that it is Monotheism; therefore, it is better to limit the explanation to it being a preparation.

(A veil) — which prevents them from perceiving you according to what you are upon of Prophethood and majesty of status. Because of this, they dared to utter the grave [statement], which is His saying: "You follow only a man bewitched." The root of hijab (veil), like hajb, is prevention from reaching; it is a verbal noun [masdar], but it is intended here as a description, meaning "a preventing [veil]."

(Hidden) — meaning having a cover. It is a derivative indicating possession [of a quality], like rajul martub (a man with moisture), makan mahul (a terrifying place), or jariya maghnujah (a coquettish girl). From this also comes "a promised fulfillment" [wa'dan ma'tiyan], and similarly, "a brimming flood" [saylun muf'am]—though the majority [in such constructions] prefer the fa'il form, such as labin (possessor of milk) and tamir (possessor of dates).

It has been permitted that the attribution [to the active/passive forms] is metaphorical, as is well-known in the latter example. Al-Akhfash suggested that maf'ul [passive participle] can come in the meaning of fa'il [active participle], as in "gushing water" [ma'in dafiq]. Thus, mastur could mean "covering" [satur]. Or, it may mean "hidden from the senses," in which case it remains upon its literal meaning, serving as an explanation that the veil is metaphysical, not physical. Or, it may mean "hidden in itself by another veil," which serves as an indication of the multiplicity of veils. Or, it may mean "hidden in its being a veil," as they do not know that they do not know. It is also said that it is a case of elision and prepositional connection, meaning: the Messenger (peace be upon him) is hidden by it.