The human heart carries a light that lets a person recognise truth and tell right from wrong, but sin can cover that light. Writing in Ad-Da' wa ad-Dawa, the classical scholar Ibnu Qayyim al-Jauziyyah explains how wrongdoing slowly darkens the heart. The teaching, published by Republika, also ties persistent sin to a weakened body and a fading ability to obey God's commands. Someone who keeps sinning, the text warns, loses the sensitivity that once steered them toward good.