Tafsir Ibn Abbas: Al-Waaqia, Ayah 87

do you not bring it back why do you not restore the spirit to the body after it has reached the throat if you are truthful? in what you claim the second law-lā ‘why … if’ is repeated to emphasise the first one; idhā ‘when’ is an adverbial particle qualifying tarji‘ūna ‘bring it back’ to which both conditions are semantically connected. The meaning is ‘Why do you not bring it back when in repudiating resurrection you are being truthful in this repudiation?’ That is to say ‘Let death also be repudiated as impossible in its case just as you claim that resurrection is impossible’.