Warning against heedlessness and complacency

هَلْ يَنظُرُونَ إِلَّا ٱلسَّاعَةَ أَن تَأْتِيَهُم بَغْتَةً وَهُمْ لَا يَشْعُرُونَ

Are they waiting except for the Hour to come upon them suddenly while they perceive not?