"In it you have"—meaning: in that book—"whatever you choose," meaning: what you select. The lam (letter l) is a connector (sila); meaning: you do not have a book in which you read that you will indeed have whatever you choose.
﴿ان لكم فِيهِ﴾ فِي ذَلِكَ الْكِتَابِ ﴿لَمَا تَخَيَّرُونَ﴾ أَيْ: مَا تَخَيَّرَونَ وَاللَّامُ صِلَةٌ؛ أَيْ: لَيْسَ عِنْدَكُمْ كتابٌ تَقْرَءُونَ فِيهِ إِنَّ لَكُمْ لَمَا تَخَيَّرُونَ
