بَلْ هُوَ ءَايَٰتٌۢ بَيِّنَٰتٌ فِى صُدُورِ ٱلَّذِينَ أُوتُوا۟ ٱلْعِلْمَ … أَوَلَمْ يَكْفِهِمْ أَنَّآ أَنزَلْنَا عَلَيْكَ ٱلْكِتَٰبَ يُتْلَىٰ عَلَيْهِمْ
"No; rather it is clear signs in the breasts of those who have been given knowledge… Is it not enough for them that We have sent down to you the Book that is recited to them?"
I record this as an observation: in the preceding verse (48) it was said that the acts of writing and reading were absent. This verse specifies the place in which the text is carried — and the place specified is not a writing surface but memory.
أَوَلَمْ يَكْفِهِمْ — "is it not enough for them?" The question comes after a demand for a miracle (50: law lā unzila ʿalayhi āyātun min rabbih).
And the construction of the answer is worth recording: the demand is not refused; what answers it is pointed out: a book that is recited is already there.
This comes from the same place as the line of proof treated at al-Aḥqāf 46/4 and at Luqmān 31/10: the proof demanded is compared with the one already in hand.
وَيَسْتَعْجِلُونَكَ بِٱلْعَذَابِ وَلَوْلَآ أَجَلٌ مُّسَمًّى لَّجَآءَهُمُ ٱلْعَذَابُ (53) — demanding haste.
The construction ajalun musammā was treated at al-Aḥqāf 46/3, al-Zumar 39/42, Fāṭir 35/45 and Luqmān 31/29. The same thing is said in all five places, and here a further function of it appears: the reason for the delay.
وَإِنَّ جَهَنَّمَ لَمُحِيطَةٌۢ بِٱلْكَٰفِرِينَ (54) — muḥīṭa (encompassing). The root ح-و-ط was treated at al-Baqara 2/255 and at Fuṣṣilat 41/54.