When Lord Shiva dance, he did not dance for the audience or for the appreciation. He did not even dance for the music. He danced with the divine energy. His dance was guided by an enormous force which he found in himself. The Great Nataraj pose helps us to ask respectfully for that energy.
Dance is Divine as a blessing. Everything in this world works in a rhythm, even the most complex and spontaneous chemical reactions works in a rhythm, we just have to find it. Every one has got dance in them. The process of learning classical dance is to find that divine energy in yourself. Everything done without it will be artificial, and the bhav will also be artificial. A dance without bhav is like a body without a soul.
You need energy for everything. There is enormous energy within you. Once you connect yourself to the divine source of energy the bhav comes of its own. Learning Classical dance is the process of reaching that energy.