وَيَقُولُ الَّذِينَ كَفَرُوا لَوْلَا أُنزِلَ عَلَيْهِ آيَةٌ مِّن رَّبِّهِ ۗ قُلْ إِنَّ اللَّهَ يُضِلُّ مَن يَشَاءُ وَيَهْدِي إِلَيْهِ مَنْ أَنَابَ (27)
(13:27) Those people who have rejected (Muhammad as a Prophet) say, "Why has no Sign been sent down to him from his Lord? *43 -Say, "Allah leads astray whom He will; and He leads to Himself only those who turn to Him. " *44
*43) Please also keep in view the answer that has been given to this question in v.7.
*44) This is the answer to their question. It is not due to the lack of signs that they were going astray, but it is the lack of any desire in them to seek right guidance. For Allah dces not force one to follow the Right Way, if he deliberately turns away from it. He lets such persons wander on the wrong ways they choose to wander. Nay, even all those things that should serve as a means to guidance for a seeker of truth, become the means of deviation for the one who seeks deviation. So much so that that very torch which helps show the way to the former, dazzles the eyes of the latter. This is how Allah Leads astray a person.
This answer to the demand of a Sign is matchless in its eloquence. It says to them, "O foolish people! it is not due to the lack of Signs that you are not finding the right path, but it is due to the lack of any desire in you for it. You do not see any of the countless Signs that lie scattered all around you because you have no desire to go to the Right Way. How can then any Sign be helpful to you ? For you would not see any of those Signs. However, those who seek the Right Way to Allah, see these Signs and find the Right Way with their help."