śraddhā māṁ tatra cārcayet
sarva-bhūteṣv ātmani ca
The Supreme Personality of Godhead is worshiped according to the faith of a particular worshiper. The Deity form, arcā, is specifically mentioned here because Deity worship is essential for spiritual progress. Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura mentions that inexperienced persons may think that the Deity is meant for the sense gratification of the worshiper, since superficially the Deity is made of external substances such as marble or brass. But through the process of installing the Deity by chanting of authorized mantras, one invites the Supreme Personality of Godhead to enter the Deity form. By regulated, faithful worship one gradually understands that the Deity is completely nondifferent from the Supreme Lord Himself. At that stage, on the strength of Deity worship, one rises to the second-class platform of devotional service. At this more developed stage one desires to make friendship with other devotees of the Lord, and as one becomes solidly established in the community of Vaiṣṇavas, one completely gives up material life and gradually becomes perfect in Kṛṣṇa consciousness.