The study aims to describe the meaning of mu`min and kāfir in the Qur'an and its implications for Islamic education. The study method uses the thematic digital Qur`an approach. The study found that, the meaning of mu`min and kāfir refers to the main character of a person. If he is characteristically obedient to God, he is a mu`min (believer). On the contrary, if he has the character of disobeying against God's main command, then he is a kāfir (infidel). So far many Muslims have been wrong. They claim every Muslim is automatically mu'min while everyone outside of Islam is an infidel. Even those who radically accuse Muslims of being outside of the mainstream as infidels too. So, it could be a Muslim who rejects the main commandment of the Prophet sentenced as an infidel by God while an Ahl al-Kitāb assessed as a mu`min. The implication is that religious education needs to be done to build true faith and religious tolerance.