وَإِذْ قَالَ لُقْمَانُ لِابْنِهِ وَهُوَ يَعِظُهُ يَا بُنَيَّ لَا تُشْرِكْ بِاللَّهِ ۖ إِنَّ الشِّرْكَ لَظُلْمٌ عَظِيمٌ

This verse records the wise counsel of Luqman to his son, beginning with the most fundamental teaching in Islam: the oneness of Allah. Luqman characterizes associating partners with Allah (shirk) as "great injustice" because it involves giving the rights that belong exclusively to the Creator to created beings. This injustice is against Allah, against oneself, and against the natural order. The verse emphasizes the importance of parents teaching their children about monotheism as the foundation of all other teachings. It shows that the first and most crucial lesson a parent can give their child is proper understanding of Allah's uniqueness and sovereignty.