Deep rest is bliss, and bliss is the understanding that only God exists. Knowing that only God exists is the deepest rest possible. This conviction or experience that "only God exists" is Samadhi. Samadhi is the mother of all talents, strengths and virtues. Samadhi is needed even for the most materialistic person because a materialistic person looks to gain strength and virtues. To be in Samadhi you do not need any effort or talents, strengths or virtues.
Withdrawing from all types of physical and mental activity is rest. That is in-built in our system as sleep, and sleep is the best friend of activity. Samadhi is a conscious rest. Samadhi is the best friend of life. To be alive in your full potential, Samadhi is indispensable.