The playing child is the imaginative child. He or she can imagine alternatives to a threatening or unfair situation and is far less prone to violence as a solution than a child who can't play. The child who has no inner world of images to draw on can't imagine alternatives to his immediate sensory world, and so has no hope of changing times.
Without imagination the child will not be able to grasp abstract issues or subjects later. Unable to see the boat or truck in the matchbox, the child will be unable to "see" alternatives to violence when the going gets rough; he will not be able to "See" with the inner eye what the outer mathematical symbol stands for; he will not be able to "see" a solution unless that solution is presented graphically from without.
So nature's prime agenda in childhood is to develop imagination-ability to create images not present to the sensory system, and this takes place through storytelling and imaginative play.