"Mayavadis and atheists accept the forms of the Deities in the temple of the Lord as idols, but devotees do not worship idols. They directly worship the Personality of Godhead in His arca incarnation. Arca refers to the form which we can worship in our present condition. Actually, in our present state it is not possible to see God in His spiritual form because our material eyes and senses cannot conceive of a spiritual form. We cannot even see the spiritual form of the individual soul. When a man dies we cannot see how the spiritual form leaves the body. That is the defect of our material senses. In order to be seen by our material senses, the Supreme Personality of Godhead accepts a favorable form which is called arca-vigraha. This arca-vigraha, sometimes called the arca incarnation, is not different from Him. Just as the Supreme Personality of Godhead accepts various incarnations, He takes on forms made out of matter -- clay, wood, metal and jewels."
(Srimad-Bhagavatam, 3.25.35, Purport)
(*Many thanks to Mother Devavati for submitting the beautiful Deity photos from New Vrindaban and Gita Nagari.)