THE fact that the form of a spirit-person is the human form or that a spirit is a person as far as form is concerned follows from what has been presented in a number of the earlier chapters, especially where I explained that every angel is in a perfect human form (Sections 73–77), that everyone is a spirit inwardly (Sections 432–444), and that the angels in heaven are from the human race (Sections 311–317).
This may be grasped even more clearly from the fact that we are human because of our spirit, not because of our body, and because our physical form is appended to the spirit in keeping with its form, not the other way around, since a spirit is clothed with a body that suits its form. As a result, the human spirit acts upon the individual parts of the body, even the smallest ones, even to the point that any part that is not activated by the spirit, any part in which there is no spirit acting, is not alive. Anyone may realize this by considering that thought and intent activate absolutely everything in the body and are so completely in control that nothing dissents, and that if anything does not consent it is not part of the body. It is actually expelled as something with no life in it. Thought and intent are attributes of our spirit, not of the body.
The reason we cannot see the human form of spirits who have left the body and spirits still within the people we meet is that our physical organ of sight, the eye, is material to the extent that it can see in this world, and what is material sees only what is material. What is spiritual, though, does see what is spiritual; so when the material eye is covered over and loses its coordination with the spirit, then spirit is visible in its own form. This is a human form not only for spirits who are in the spiritual world but also for spirits in people we meet while they are still in their bodies.
from Heaven and Hell, Section 453