Monotheism (Tawhid) as the foundation of all righteous deeds

ذَٰلِكَ هُدَى ٱللَّهِ يَهْدِى بِهِۦ مَن يَشَآءُ مِنْ عِبَادِهِۦ ۚ وَلَوْ أَشْرَكُوا۟ لَحَبِطَ عَنْهُم مَّا كَانُوا۟ يَعْمَلُونَ

That is the guidance of Allāh by which He guides whomever He wills of His servants. But if they had associated others with Allāh, then worthless for them would be whatever they were doing.