the proof of it is in the listener

Trances and visions induced by words, or drugs, or any other sensory or mental means are temporary and inconclusive. The truth of what is said here is immovable and everlasting. And the proof of it is in the listener, in the deep and permanent changes in his entire being. It is not something he can doubt, unless he doubts his own existence, which is unthinkable. When my experience becomes your own experience also, what better proof do you want?