The Lord’s Word makes it clear that many people used to talk with spirits and angels, and that they heard and saw much in the other world, but that heaven was later shut, so to speak. It was closed so tightly that today hardly anyone believes spirits and angels exist, let alone that anyone can talk with them. To most people’s way of thinking, speech with invisible beings (whose existence they deny at heart) is impossible.
In the Lord’s divine mercy, however, I have been granted the almost continuous opportunity for several years now to hold conversations with them and to go among them as one of them. Let me report here, then, what I have had the privilege of learning about the way they talk to each other.
When spirits talked to me, I heard them as clearly and distinctly as the people I speak with on earth. In fact when I talked with spirits while surrounded by people, I noticed that I could hear the spirits just as audibly as the people—so much so that the spirits sometimes had trouble believing they could not be heard by my companions. There was no difference whatever in the sound.
But since spirits’ speech stimulates the ear’s inner organs in a different way than conversation with other people does, it was inaudible to everyone but me, in whom those organs were open, by the Lord’s divine mercy. Human speech enters through the ear along an external route, by means of the air. The speech of spirits enters not by the ear or the air but by an inner way. It reaches the same organs inside the head (in the brain), which is why it sounds the same.
from Secrets of Heaven, Volume 2, Sections 1634, 1635