Sri-vigraharadhana-nitya-nana-srngara-tan-mandira-marjanadau (Sri-gurvastaka 3). The vigraha, the Deity of Krsna, appears by Krsna's mercy. Because Krsna is alaksya, invisible, He becomes visible to give the world the facility to see Him.

It is not that Krsna is stone, wood, or metal. Krsn'a is always Krsna, but because One cannot see anything beyond material elements like wood, stone, and metal, He appears in a form made of these elements. But He is neither wood, metal, nor stone. When One associate with the Deity, One actually associate with Krsna personally. Because Krsna is invisible, He very kindly takes a form that is visible to mankind. This is Krsna's mercy.

One should never think, 'Oh, here is a stone Krsna.' Krsna is everything, and therefore Krsna is stone also, but He is not the kind of stone that cannot act. Even in the form of stone or metal, Krsna can act as Krsna, and one who worships the Deity will perceive that. Svayam eva sphuraty adah. The Deity, although apparently stone, may speak with a devotee. There are many instances in which this has happened.

(Teachings of Queen Kunti, Chapter 4) -