This body is a loan that you have taken from Mother Earth. She is very generous with this, but when it comes to reclaiming, she is very stringent. She will not let you take even one atom as a souvenir. She will collect every atom back. So the yogis learned how to steal from the Earth. That is, they convert the physical into the non-physical. Now, she cannot claim it back. She cannot recognize it. This non-physical thing is known as ojas.
