The text also identifies alerting someone to error (التنبيه على الخطأ). An addressee may have misidentified or wrongly characterized a group or person. A relative clause can bring forward a decisive characteristic that corrects that assumption.
Teaching example:
Someone calls a group ignorant. The reply is: «الذين علّموا الناس سنين كثيرة هم هؤلاء» — These are the people who taught others for many years.
The clause «علّموا الناس» directly challenges the mistaken description. Its chief function is not bare identification but correction of an erroneous judgment.