Talking with spirits is rarely allowed nowadays, though, because it is dangerous. The spirits then actually know that they are with us, which otherwise they would not; and evil spirits by nature harbor a murderous hatred for us and crave nothing less than our total destruction, body and soul. This is what actually goes on in people who regularly lose themselves in delusions, even to the point that they lose touch with the pleasures appropriate to their natural person.
There are some people who lead solitary lives who sometimes hear spirits talking with them without risk; but the Lord keeps these spirits a little space away so that they do not know they are with these individuals. Most spirits, you see, are not aware that there is any other world than the one they are living in or therefore that there are people anywhere else. So we are not allowed to talk back to them, since if we did, they would know.
People who are constantly thinking about religious matters, so wrapped up in them that they practically see them within themselves, also begin to hear spirits talking with them. This is because when we voluntarily get wrapped up in religious matters, no matter what kind, without the interruption of various useful activities in the [external] world, these matters enter into us very deeply and take substance there so that they occupy our whole spirit, move into the spiritual world, and affect spirits there. However, people like this are visionaries or fanatics, and no matter what spirit they hear, they believe it is the Holy Spirit, even though the spirits they hear are fanatical. Spirits like this see false things as true; and because they see them as true they convince themselves and also convince the people into whom they flow. Further, since spirits like this who command obedience have also begun to urge people to do evil things, they have gradually been moved away. Fanatical spirits can be differentiated from other spirits by the fact that they believe they are the Holy Spirit and that what they are saying is divine. They do not harm us, because we offer them divine worship.
I have talked with them on occasion and the unspeakable things they instill into their worshipers have come to light. They live all together toward the left, in a desert area.
from Heaven and Hell, Section 249