There will only be a single jerk, and they will gape,
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Tafseer
'Abdullāh Ibn 'Abbās / Muḥammad al-Fīrūzabādī
تفسير : (there is but one shout) it is but one single blow, which is the blowing of the resurrection, (and lo!) they emerge from the graves and (they behold) what they will be commanded to do.
Jalāl al-Dīn al-Maḥallī
تفسير : for it will be only (innamā hiya, this [hiya] is a demonstrative pronoun explained by [the following, zajratun) a single cry and, lo! they, all creatures, will be, alive, watching, [to see] what will be done with them.