Actually, that is a false statement. The nervous system is a very fast acting control system.
In mammals, including humans, the nervous system is comprised of the brain, spinal cord, and nerves. The nerves consist of neurons, or nerve cells. Its purpose is the coordination and control of the body. It functions by reacting to stimuli inside and outside of the body. Stimuli are any changes that occur which the body needs to respond to in order to maintain homeostasis.
The central nervous system performs the function of relaying nerve messages, analyzing information and processing information so that a response can occur. The peripheral nervous system transmits impulses between the surroundings and the central nervous system.
If an organism is unable to respond to changes, whether inside its body or outside in its surroundings, it can lead to death. A response needs to be very rapid in order to be effective.
For instance, if an automobile is speeding towards a person, their sense organs will see and hear the oncoming auto, send an impulse to the spinal cord, which will send another impulse to nerves in the legs to stimulate muscles which will allow the person to jump out of the way. All of this is done extremely fast and is called a reflex. Reflexes allow the body to quickly respond to dangerous situations without having to waste precious time to think them through. Later, another message to the brain will let someone realize what just happened.
To summarize, the action of the nervous system is very rapid in order to maintain homeostasis within the organism's body and to keep an organism safe in its environment.