From the Johannes Greber book "Communication With the Spirit World Of God -- Its Laws and Purpose" :
You are right to ask me who I am, for it is your first duty to test the spirits that speak to you and to assure yourself that they were sent by God ... I swear to you before God that I am one of His good spirits , indeed one of His highest spirits, but my name keep to yourself ... From the days of the first man down to the present, the spirit-world has communicated with mankind. That is true of both the good spirit-world and the bad. ... [T]he World of spirits, which is separated from you materially, has various ways of communicating with you by means perceptible to your senses ... [W]hen the Bible says: "God spoke", it was not God himself who spoke, because as a rule, God speaks only through his spirit-messengers.
What page(s) is this quote from? (I don't have an actual copy of the book myself)