The Vaiṣṇavite scriptures which preach the cult of Viṣṇu-Nārāyaṇa-Kṛṣṇa put forth the theory that the Supreme Lord Viṣṇu has four kinds of manifestations:
Out of these, the arcā represents the images or icons installed and worshipped ceremonially in temples and shrines. Such icons are classified into four groups: svayaṁvyakta or self-manifested, daiva or established by gods, ārṣa or consecrated by the ṛṣis (sages) and mānuṣa or prepared by human beings.
Even the man-made images, though prepared out of inanimate substances, can become ‘alive’ if they are duly consecrated through the prescribed rites. God who is omnipotent ‘descends’ into such images with a subtle body. This is the ‘arcāvatāra’ or incarnation for purposes of ordinary worship.