A bare demonstrative such as “these people” often fails to correct a mistaken description: it identifies without highlighting the contrary evidence. A relative expression can put the very fact that challenges the error before the hearer.
«هؤلاء حاضرون» — They are present: announces presence without correcting a belief.
«الذين اجتهدوا في التعليم حاضرون» — Those who labored in teaching are present: foregrounds work the addressee may have denied.
Placing the corrective clause before the predicate can adjust the hearer's prior understanding. The clause is not automatically a formal proof, however; its force is contextual.