Bhuta Shuddhi is an important part of tantric worship and is performed before the worship of a deity in Tantrism. The human body is made of five bhutas or elements – earth, water, fire, air and vaccum or ether.
By purifying the five bhutas a tantric aspirant transforms his body into a divine form. The aspirant does this ritual so that the body can be fit to be an abode of the deity.
Primarily the body is cleansed so that it can be fit for the deity to enter it and reside in it.
Bhuta Shuddhi is attained by smearing body with ash, sprinkling it with water, reciting mantras and through breath control or pranayama.
It is one among the eight external steps in Tantra. It is known as Bahya Upasana.