The sudden arrival of divine retribution

وَلَا يَزَالُ ٱلَّذِينَ كَفَرُوا۟ فِى مِرْيَةٍ مِّنْهُ حَتَّىٰ تَأْتِيَهُمُ ٱلسَّاعَةُ بَغْتَةً أَوْ يَأْتِيَهُمْ عَذَابُ يَوْمٍ عَقِيمٍ

But those who disbelieve will not cease to be in doubt of it until the Hour comes upon them unexpectedly or there comes to them the punishment of a barren Day.