إِنَّ الْعَمَلَ الصَّادِقَ أَبْقَى أَثَرًا مِنْ قَوْلٍ تَذْهَبُ بِهِ الرِّيحُ.
Sincere action has a more enduring effect than words carried off by the wind.
Inna reinforces the conclusion, and abqā atharan sets lasting impact as the basis of comparison. Words dispersed by wind supply the opposing image: a fleeting utterance against enduring consequences.
Inna alone does not establish that the listener is fiercely denying the claim. Reinforcement may mark an important conclusion after an argument, as it does here.