We must genuinely recognize the value of Krishna consciousness through our own internal experience if we want to distribute Krishna consciousness. Of course, by distributing Krishna consciousness and preaching, we get realization and conviction. This is the method by which Srila Prabhupada taught us to become Krishna conscious, but we should never neglect our sadhana and the cultivation of our internal life in the name of preaching. When our lives are balanced nicely in this way, we will have the strength to go on preaching.
(Collected Letters to My Disciples, Vol 3, Pg 106 last Paragraph)