A preacher must have an internal life as well if he wants to continue to preach. This means we must always be trying to improve the quality of our chanting. We should chant with a serious desire to make progress in devotional service. We should be careful to not allow our chanting to become routine, ritualistic chanting. When we chant, we should chant with a desire to chant purely, without any offense, free from anarthas. This requires practice, and it must be practiced daily.
(Collected Letters to My Disciples, Vol 3, Pg 58 last paragraph )