"And He is competent to assemble them when He wills," meaning: He will assemble them on the Day of Resurrection.
﴿وَهُوَ عَلَى جَمْعِهِمْ إِذَا يَشَاء قَدِيرٌ﴾ يَعْنِي: أَنه يجمعهُمْ يَوْم الْقِيَامَة
