Why do we have to obtain Nirvana while in this physical body?

Sri Sri:To cleanse the other two spaces, because once we leave the spirit, the mind leaves this body; the mind can not be cleansed outside there. It can not be rid of any thoughts out there, once out of the body. So the body is the instrument in which the space can wash itself out from past impressions. And that is what the Buddha called the nirvana it is here and be in your space and that you are nobody and nothing.