The conversation between Lord Śrī Kṛṣṇa and the brāhmaṇa is proof that the Lord in His arcā-mūrti, or form made of material elements, is not material, for those elements, although separated from the Lord, are also a part of the Lord’s energy, as stated in the Bhagavad-gītā. Because the elements are the Lord’s own energy and because there is no difference between the energy and the energetic, the Lord can appear through any element. Just as the sun can act through the sunshine and thus distribute its heat and light, so Kṛṣṇa, by His inconceivable power, can appear in His original spiritual form in any material element, including stone, wood, paint, gold, silver and jewels, because the material elements are all His energy. The śāstras warn, arcye viṣṇau śilā-dhīḥ . . . nārakī saḥ: one should never think of the arcā-mūrti, the Deity within the temple, as stone, wood or any other material element. Because of his advanced devotional position, the younger brāhmaṇa knew that although the Deity of Gopāla appeared to be stone, He was not stone. He was the son of Nanda Mahārāja, Vrajendra-nandana Himself.
As such, the Deity can act exactly as the Lord did in His original form as Kṛṣṇa. Lord Kṛṣṇa was talking to the young brāhmaṇa just to test his knowledge about the arcā-vigraha. In other words, those who have understood the science of Kṛṣṇa – Kṛṣṇa’s name, form, quality and so forth – can also talk with the Deity. To an ordinary person, however, the Deity will appear to be made of stone, wood or some other material. In the higher sense, since all material elements ultimately emanate from the supreme spiritual entity, nothing is really material. Being omnipotent, omnipresent and omniscient, Kṛṣṇa can deal with His devotees in any form without difficulty. By the mercy of the Lord, the devotee knows perfectly well about the Lord’s dealings. Indeed, he can talk face to face with the Lord.
Ref >> Srila Prabhupada Vani.