In the name of Allah the Most Beneficent the Most Merciful,
إِنَّ فِي ذَلِكَ لَذِكْرَى لِمَن كَانَ لَهُ قَلْبٌ أَوْ أَلْقَى السَّمْعَ وَهُوَ شَهِيدٌ
“Indeed in that is a reminder for whoever has a heart or who listens while he is present [in mind].”
Dear reader the meaning is (and Allah knows best) that there is indeed a reminder for the one who hears the speech,comprehends and understands it in his mind and grasps its indications with his mind.
Mujahid (a Quranic exegete from the early generations) said ‘or gives ear’ means he does not talk to himself but listens with an attentive heart.
Thus either one should have so much of native intelligence as to think on their own or otherwise one should be so free from prejudice&neglect so as to listen attentively.
For sense and sanity to make its way to a person they must possess a sound heart/intellect and listen attentively.Therefore a lot of lessons can be learnt from the previous lessons in the Surah for one with a sound intellect and who listens attentively and Allah knows best.
Asalaam aleykum warahmatullahi wabarakatuh.(may peace and the mercy and blessings of Allah be upon you)