وَإِذَا تُتْلَىٰ عَلَيْهِمْ ءَايَٰتُنَا بَيِّنَٰتٍ مَّا كَانَ حُجَّتَهُمْ إِلَّآ أَن قَالُوا۟ ٱئْتُوا۟ بِـَٔابَآئِنَآ إِن كُنتُمْ صَٰدِقِينَ
"And when Our signs are recited to them clearly, their only argument is to say: 'Bring back our forefathers, if you are truthful!'"
The construction of the sentence must be recorded: the verse names the words spoken as ḥujja (argument) — and limits it with illā: they have no other argument.
حُجَّة — root ح-ج-ج: to head towards a goal, to intend; and a word that binds the other party. The word's sense of "proof" comes from its dragging the opposing party to a certain place in a dispute.
I record this as my own reading: the verse does not begin by saying that what is said is not an argument; it counts it as an argument and reports it as such, and leaves its weakness before the reader. The demand is this: let the dead forefathers now be brought back.
This demand had occurred in the same form in al-Aḥqāf at 46/17 (fa'tū bi-ābāʾinā in kuntum ṣādiqīn) and was treated there: the objection is framed by choosing the hardest example.
قُلِ ٱللَّهُ يُحْيِيكُمْ ثُمَّ يُمِيتُكُمْ ثُمَّ يَجْمَعُكُمْ إِلَىٰ يَوْمِ ٱلْقِيَٰمَةِ — and the answer does not meet the demand: it recalls the sequence.
Three verbs, joined by thumma: He gives life → He gives death → He gathers. In Arabic thumma conveys an interval; that is, there is time between the three verbs. The difference between what is demanded (bring them now) and what is announced (they are gathered at an appointed time) lies exactly in this particle.
The same answer had been given with the same word in al-Wāqiʿa at 56/49-50 (la-majmūʿūna ilā mīqāti yawmin maʿlūm) and was treated there: the gathering is tied not to a place but to a time.