لَقَدْ أَنزَلْنَآ إِلَيْكُمْ كِتَـٰبًا فِيهِ ذِكْرُكُمْ ۖ أَفَلَا تَعْقِلُونَ
Laqad anzalnaaa ilaikum Kitaaban feehi zikrukum afalaa ta'qiloon
Indeed, we have sent down to you a book in which is your reminder. Will you not then use reason?
Dhikr does two jobs across these lines. At 21:7 the word stands for the earlier scripture, and the Meccans are sent to ask the people who hold it; now a book comes down in which the reminder belongs to them, and the possessive carries the weight. Commentators take fīhi dhikrukum both as your reminder and as your standing, the mention that raises a people, which is how 43:44 uses the word of the same book.