That is the guidance of Allah by which He guides whomever He wills of His servants. But if they had associated others with Allah, then worthless for them would be whatever they were doing.
ذَٰلِكَ هُدَى اللَّهِ يَهْدِي بِهِ مَنْ يَشَاءُ مِنْ عِبَادِهِ ۚ وَلَوْ أَشْرَكُوا لَحَبِطَ عَنْهُمْ مَا كَانُوا يَعْمَلُونَ