Spirits who are below heaven are amazed when they hear and see that heaven is both below and above them. They have had the faith and opinion common to people in this world that heaven is only overhead. They do not really know that the locations of the heavens are like the locations of the members and organs and viscera in a human being, with some above and some below, and that it is also like the locations of the parts within each member and outer or inner organ, with some within and some outside. This is the reason for their confusion about heaven.
We have presented these statements about heaven as the universal human because without them as preface there can be no comprehension whatever of the things about heaven that are to follow. No clear concept of heaven can be gained, either, no clear concept of the union of the Lord with heaven, of the union of heaven with us on earth, of the inflow of the spiritual world into the natural world, and none whatever of correspondence, all of which must be discussed in sequence in the pages that now follow. This material has been presented first, then, to shed light on these matters.
from Heaven and Hell, Sections 66,67