The Ganges, emanating from the toe of Lord Vishnu, purifies the three worlds, the upper, middle and lower planetary systems. Similarly, when one asks questions about the pastimes and characteristics of Lord Vasudeva, Krishna, three varieties of men are purified : the speaker or preacher, he who inquires, and the people in general who listen.
One can gradually become purified by seeing, touching and worshiping temple deities, places of pilgrimage and holy rivers. but one can attain the same result immediately simply by receiving the glance of exalted sages.
Purification means bringing something back to its natural state. Just like pure water means there is no contamination in it.
By one's engaging in the processes of demigod worship, austerities, breath control, compassion, bathing in holy places, strict vows, charity, and chanting of various mantras, one's mind cannot attain the same absolute purification as that achieved when the unlimited Personality of Godhead appears within one's heart.