The ability to inspire others comes from purity. Wherever there is real Krishna consciousness, we will find an awakening of spiritual desire. Desire is the natural and eternal companion of the soul. Therefore, it is natural for every living entity to want to do something. We simply have to steer them in the proper direction, pointing them always toward Krishna. Therefore we have to preach purely. There is no greater force than pure preaching.
Lectures from a disciple Vol 1, Pg 335 1st paragraph.