God puts the souls to death when the end of their life comes, and also at the time of sleep. Thus, He takes some back during their sleep, while others are allowed to continue living until the end of their predetermined interim. This should provide lessons for people who reflect.
اللَّهُ يَتَوَفَّى الأَنفُسَ حينَ مَوتِها وَالَّتى لَم تَمُت فى مَنامِها فَيُمسِكُ الَّتى قَضىٰ عَلَيهَا المَوتَ وَيُرسِلُ الأُخرىٰ إِلىٰ أَجَلٍ مُسَمًّى إِنَّ فى ذٰلِكَ لَـٔايٰتٍ لِقَومٍ يَتَفَكَّرونَ
allaahu yatawaffal anfusa heena mawtihaa wallatee lam tamut fee manaamihaa fa yumsikul latee qadaa ‘alaihal mawta wa yursilul ukhraaa ilaaa ajalim musammaa; inna fee zaalika la Aayaatil liqawmai yatafakkarroon