na hy am-mayāni tīrthāni
na devā mṛc-chilā-mayāḥ
te punanty uru-kālena
darśanād eva sādhavaḥ
na -- not; hi -- indeed; ap -- of water; mayani -- composed; tirthani -- holy places; na -- not; devah -- deities; mrit -- of earth; sila -- and stone; mayah -- composed; te -- they; punanti -- purify; uru-kalena -- after a long time; darsanat -- by being seen; eva -- only; sadhavah -- saints.
Because the Personality of Godhead is absolute -- the Supreme Spirit -- any representation of Him, whether manifested in stone, paint, sound or any other authorized medium, is nondifferent from His original form in the topmost spiritual planet, Goloka Vrindavana. But ordinary demigods are not absolute, being infinitesimal spirit souls, and thus representations of the demigods are not identical with them. Worship of demigods or ritual bathing in a sanctified place gives only limited benefit to those who lack transcendental faith in the Supreme Lord.
On the other hand, great Vaishnava saints like Vyasadeva, Narada and the four Kumaras are always absorbed in Krishna consciousness, and thus they are veritable moving tirthas, places of pilgrimage. Even a moment's association with them, especially by hearing their glorification of the Lord, can deliver one from all material entanglement. As King Yudhishthira said to Vidura,
bhavad-vidha bhagavatas
tiritha-bhutah svayam vibho
tirthi-kurvanti tirthani
svantah-sthena gadabhrita
"My Lord, devotees like your good self are verily holy places personified. Because you carry the Personality of Godhead within your heart, you turn all places into places of pilgrimage." (Bhag. 1.13.10)