Hardness of the heart (qaswat al-qalb)

فَلَوْلَآ إِذْ جَآءَهُم بَأْسُنَا تَضَرَّعُوا۟ وَلَـٰكِن قَسَتْ قُلُوبُهُمْ وَزَيَّنَ لَهُمُ ٱلشَّيْطَـٰنُ مَا كَانُوا۟ يَعْمَلُونَ

Then why, when Our punishment came to them, did they not humble themselves? But their hearts became hardened, and Satan made attractive to them that which they were doing.

وَلَقَدْ صَرَّفْنَا فِى هَـٰذَا ٱلْقُرْءَانِ لِيَذَّكَّرُوا۟ وَمَا يَزِيدُهُمْ إِلَّا نُفُورًا

And We have certainly diversified [the contents] in this Qur’ān that they [i.e., mankind] may be reminded, but it does not increase them [i.e., the disbelievers] except in aversion.