Verse 21

وَمَا كَانَ لَهُۥ عَلَيْهِم مِّن سُلْطَـٰنٍ إِلَّا لِنَعْلَمَ مَن يُؤْمِنُ بِٱلْـَٔاخِرَةِ مِمَّنْ هُوَ مِنْهَا فِى شَكٍّ وَرَبُّكَ عَلَىٰ كُلِّ شَىْءٍ حَفِيظٌ

And he had no authority over them; however, this is in order for Us to know who believes in the Hereafter and who is doubtful regarding it. And your Lord is the Guardian of all things.