When is a person Krsna Consciousness enough to preach? Srila Prabhupada encouraged us to preach immediately, regardless of our degree of realization. By preaching we cement our understanding. Hearing is the first step in devotional service, and the second step is chanting. Either privately or Congregationally. Preaching really means teaching.
It is commonly accepted that by teaching others your own understanding becomes enhanced. They also say your retention levels increase when you pass on to