أَلَمْ تَعْلَمْ أَنَّ ٱللَّهَ يَعْلَمُ مَا فِى ٱلسَّمَآءِ وَٱلْأَرْضِ إِنَّ ذَٰلِكَ فِى كِتَٰبٍ إِنَّ ذَٰلِكَ عَلَى ٱللَّهِ يَسِيرٌ
A-lam taʿlam anna'llāha yaʿlamu mā fi's-samāʾi wa'l-arḍ · Inna dhālika fī kitāb · Inna dhālika ʿala'llāhi yasīr
"Do you not know that God knows what is in the heaven and the earth? That is in a book. That is easy for God."
The pattern a-lam tara (have you not seen?) occurred three times in the sūra: 18, 63, 65. Here the pattern changes: a-lam taʿlam — "do you not know?"
I record this as an observation about word order, and its ground is the change of verb: in the three earlier places something visible was being shown to the addressee — a world prostrating, the greening ground, the running ship. Here there is nothing to show: the subject is knowledge itself. And the verb changes accordingly.
إِنَّ ذَٰلِكَ فِى كِتَٰبٍ — "that is in a book". The word is indefinite: "a book". Which book is not said.
It is transmitted that in the classical commentaries this expression is taken to indicate the Lawḥ-i Maḥfūẓ. I transmit this as a report; the verse itself gives no name, and no name the verse does not give is inserted in this commentary.
إِنَّ ذَٰلِكَ عَلَى ٱللَّهِ يَسِيرٌ — the root ي-س-ر: ease. The root was treated at al-Baqara 2/185 (yurīdu'llāhu bikumu'l-yusra). I rely on that treatment. And the root will return indirectly in the last verse of this sūra: wa mā jaʿala ʿalaykum fi'd-dīni min ḥaraj.