Ms.Nixon: One of the most difficult aspects of Krishna consciousness for an outsider to accept is the Deity in the temple -- how it represents Krishna.
Could you talk a little bit about that?
Srila Prabhupada: Yes.
At the present moment, because you have not been trained to see Krishna, He kindly appears before you so you can see Him.
You can see wood and stone, but you cannot see what is spiritual.
Suppose your father is in the hospital, and he dies.
You are crying by his bedside, "Now my father is gone!" But why do you say he is gone? What is that thing which is gone?
Ms.Nixon: Well, his spirit is gone.
Srila Prabhupada: And have you seen that spirit?
Ms.Nixon: No.
Srila Prabhupada: So you cannot see spirit, and God is the Supreme Spirit.
Actually, He is everything--spirit and matter--but you cannot see Him in His spiritual identity.
Therefore, to show kindness toward you, He appears out of His unbounded mercy in the form of a wooden or stone Deity so that you can see Him.
Ms.Nixon: Thank you very much.
Srila Prabhupada: Hare Krishna!
From The Science of Self-Realization