Tafsir of An-Nazi'at 79:13

{For it is only a single shout} is a justification for an implied [statement] necessitated by their denial of that [the Resurrection]. Since the crux of the matter was their deeming the return [to life] to be difficult, this was refuted for them; thus it was said: Do not consider that return to be difficult, for it is only a single cry—meaning, [it is] brought about by a single shout, which is the second blowing [of the Trumpet]. It is expressed as such to alert [one] to the complete continuity of the [Return] with it, as if it were the very same thing. It has also been said that [the pronoun in] it refers back to "the second blowing" (al-radifah). And His saying, the Exalted...