To rest is to reflect.
Research indicates that our brains toggle between two main states: looking out at a focused task, or reflectively looking in during periods of mental downtime.
Associated with an area of the brain known as the Default Mode Network, the latter state has been found to promote higher levels of divergent, creative and reflective thinking.
It is through such thought processes that moments of daydreaming and mind wandering create space and opportunity for unexpected mental connections and creative problem-solving to occur.