The more we are happy in Krishna Consciousness the more we become purified.
How intensely we think of Krishna will determine how quickly we become purified.
One can purify the mind by the chanting process, just as one can purify gold by putting it in a fire and fanning it with a bellows.
Srimad Bhagavatam 3.28.10,
The Sankirtana movement we have started offers the best process for becoming purified of all sinful reactions and coming immediately to the platform of spiritual life.
Srimad Bhagavatam 6.2.11
By performing congregational chanting of the Hare Krishna mantra, one can destroy the sinful condition of material existence, purify the unclean heart and awaken all varieties of devotional service.
Chaitanya Caritamrta on Antya Lila 20.13
We get purified when we take anxiety for Krishna.