وَمَا كَانَ لَهُ عَلَيْهِم مِّن سُلْطَانٍAnd he (Iblis) had no authority over them,Ibn Abbas, may Allah be pleased with him said,"This means, he had no proof."إِلاَّ لِنَعْلَمَ مَن يُوْمِنُ بِالاْخِرَةِ مِمَّنْ هُوَ مِنْهَا فِي شَكٍّexcept that We might test him who believes in the Hereafter, from him who is in doubt about it.means, `We gave him power over them only to show who believes in the Hereafter and that it will come to pass.'The people will be brought to account and rewarded or punished accordingly, so that he will worship his Lord properly in this world -- and to distinguish these believers from those who are in doubt about the Hereafter.وَرَبُّكَ عَلَى كُلِّ شَيْءٍ حَفِيظٌAnd your Lord is a Watchful over everything.means, despite His watching, those who follow Iblis go astray, but by His watching and care, the believers who follow the Messengers are saved