It is declared that there are eight types of sacred images appropriate for worship in Hinduism, namely, those formed
- of stone
- of wood
- of metal
- of clay
- of sand
- of jewels
- as a painting and
- in the mind
One might well wonder: How is it possible to have devotion for a lifeless image made of material elements? In the practice of Vaishnava tantra, one learns to regard all matter as energy, shakti, of the supreme energetic, shaktiman, person, Bhagavan or Vishnu. Since all energy originates in Vishnu, he can transform or perhaps better, transubstantiate, any material substance for his own purposes, or for benefiting his devotees.
The Vaishnava tantra texts, Pancharatra Agamas, provide detailed ritual procedures for invoking Vishnu into an image, either temporarily or permanently. The aggregate of these procedures is called prana-pratishta, literally establishing life. But equally important as such formalities is the devotional attitude of the practitioner, by virtue of which her or his eyes are said to be smeared with the salve of love, enabling the practitioner to see the object of worship as the divine subject.
The ritual worship of me (Bhagavan Vishnu) in images, and so on, is done with prescribed items; yet for the desireless devotee, (ritual worship is done) with whatever items can be readily obtained, as well as by mentally fashioned offerings. (Srimad Bhagavata Purana 11.27.15).