Srimad Bhagavatam Canto 11, Chapter 03, Text 50-51


SB 11.3.50-51

arcadau hrdaye capi
nispadya proksya casanam
padyadin upakalpyatha
sannidhapya samahitah
hrd-adibhih krta-nyaso
mula-mantrena carcayet
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The devotee should gather whatever ingredients for worshiping the Deity are available, make ready the offerings, the ground, his mind and the Deity, sprinkle his sitting place with water for purification and prepare the bathing water and other paraphernalia. The devotee should then place the Deity in His proper place, both physically and within his own mind, concentrate his attention, and mark the Deity’s heart and other parts of the body with tilaka. Then he should offer worship with the appropriate mantra.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
atah sri-krsna-namadi
na bhaved grahyam indriyaih
sevonmukhe hi jihvadau
svayam eva sphuraty adah
(Padma Purana)
The Absolute Truth can never be understood by ordinary material sense perception. The conditioned souls engrossed in the vain pursuit of material sense gratification are completely indifferent to the transcendental loving service of the Lord. Their materially conditioned minds are always impure and disturbed by the endless flow of material dualities, such as prosperity and poverty, winter and summer, fame and infamy, youth and old age. Such disturbed conditioned souls cannot recognize the personal presence of the Absolute Truth in the form of the Deity.
The Lord’s incarnation as arca-avatara, the Deity form, is a special manifestation of the Lord’s mercy toward the materialistic or neophyte devotees who are still under the influence of material designations. They are unable to perceive the Lord in His eternal abode, and therefore the Lord descends as the Deity form, manifesting the prakasa incarnations and even the svayam-prakasa, or the original form of the Lord. The prakasa incarnations exhibit various pastimes within this world, whereas svayam-prakasa, the Lord’s original form, is the source of all avataras.
To one who sincerely worships the Deity, the Deity manifests Himself as the Supreme Personality of Godhead. Those who are most unfortunate cannot even recognize the Supreme Lord in His merciful Deity expansion. They consider the Deity an ordinary material object. But by surrendering at the lotus feet of a bona fide spiritual master, who is a pure devotee of the Lord, one can learn to worship the Deity, as mentioned in this verse, and thus revive one’s lost relationship with the Lord. One who considers such transcendental Deity worship to be equivalent to idol worship is grossly covered by the three modes of material nature. A person wearing rose-colored glasses sees the entire world to be rose colored. Similarly, those unfortunate living entities who are thickly covered by the material modes of nature see everything, including the Supreme Lord, as material due to their polluted vision.
Srimad Bhagavatam Canto 11, Chapter 03, Text 49
Srimad Bhagavatam Canto 11, Chapter 03, Text 52-53