Nerve cells are essential to an animal because they directly provide

Nerve cells are important to an animal as they directly provide communication between the cells.  

The most important function of nerve cells (other name - neuron) is to to transmit electrical messages and signals throughout the body. (The diagram of a neuron/nerve cell is attached).

These cells are connected to all the organs of our body via cells in muscles or glands. They received signals, pass them to the brain or their destination. Our brain controls the nervous system, and nerve cells form an important part.

If there are no nerve cells, then no signals can be passed to, no body action can be taken, life is ended.

Nerve cells are important to an animal as they directly provide communication between the cells.  

A nerve cell or a neuron refers to a cell, which conducts electrical impulses, these are the fundamental units of the nervous system. These are the cells found in the nervous system and are the unique cells developed to instigate other cells in the body in order to communicate.