Why does a desire arise? Where does it come from? What is the purpose?
All desires have got one goal, and that is happiness. If a desire brings unhappiness, it has not reached its goal. The goal of desires is to bring happiness. So, that is the purpose.
Where does it come from? It comes when you are not aware of your Being, your Self. Desire is your wanting to stay in the moment. Desire is to experience joy. Joy is only in the moment. And when you are in the moment, there is no desire. Have you noticed when you are joyful and satisfied, there is no burning desire at that time.