Verbal speech, as I said, is characteristic of people on earth and, to be specific, of their physical memory. Speech composed of thoughts, however, is the speech of spirits and, to be specific, of inner memory, which is the memory of the spirit. We are not aware that we have the latter kind of memory, because the memory of trivia belonging to the material world—physical memory—seems all-important and overshadows the inner memory. The reality, though, is that without the inner memory characteristic of our spirit, we are completely incapable of thought.
I have often used my inner memory in talking with spirits, which is to say that I have used their own language; that is, I have spoken by means of thought. The universality of the language and its richness can be seen from the fact that each word contains a whole concept of tremendous reach. As we know, it can take some time to lay out the thought behind a single word, still more the thought behind a single topic, and more yet the thought behind a constellation of topics, even if these can be brought together into a single, simple-looking composite. These considerations give some clue to the kind of speech that spirits naturally use with each other and what type of speech it is that links us to spirits.
from Secrets of Heaven, Volume 2, Section 1639