The first thing Allah (swt) speaks of after the signs of the creation of the human beings is sleep. This is because, sleeping is one of the most important things for a human being. Observe how a human being is not able to do anything at all if he is overcome by sleepiness. No research has been able to fully define the nature of sleep and its essence. Allah (swt) says:
﴾اللَّهُ يَتَوَفَّى الْأَنفُسَ حِينَ مَوْتِهَا وَالَّتِي لَمْ تَمُتْ فِي مَنَامِهَا﴿
(Allah takes the souls at the time of their death, and those that do not die [He takes] during their sleep…) (Az-Zumar: 42)
سُبَاتًا (for rest): The word “Subaat” means the separation of a human being from movement. When the human sleeps, his soul is kept within him but he is separated from movement.