If by the tongue you chant Hare Krishna mantra and by the tongue you taste prasadam, you will be perfect, simply by executing these two things.
As soon as a devotee can chant the holy name and glories of the Supreme Lord, he certainly comes to the liberated position. Attachment for glorifying the Lord by hearing and chanting the holy name and activities of the Lord (Sravanam Kirtanam Visnoh) certainly brings one to the position where material contamination is absent.
Just like we need food for the body, we need food for the soul and what is that food? Hearing and chanting God’s names in the association of saintly people. Otherwise, we will give in to temptations at the smallest instance. We will be weaklings, spiritually.
There are two types of chanting: Offensive, where the result will be that chanting will be stopped in due course of time. While the other one is offense less chanting, where we will be inspired to always chant more.
Only the most intelligent people are entitled to engage in the process of chanting the mahamantra.
While chanting, the soul should be involved, not just the mouth.