From Arcana Coelestia ~ Emanuel Swedenborg
... when the Lord
made His Human Divine He advanced in a like order to that in which He makes man
new by regeneration, namely, from what is external to interior things, thus from
the truth which is in the ultimate of order to a good which is interior, and is
called spiritual good, and from this to celestial good. But these things cannot
fall into the understanding of anyone unless it is known what the external man
and the internal man are, and that the former is distinct from the latter,
although while man is living in the body they appear as one; also unless it is
known that the natural constitutes the external man, and the rational the
internal; and further, unless it is known what the spiritual is and what the
celestial.These things have indeed already been occasionally unfolded, nevertheless they who have previously had no idea about them in consequence of having no desire to know the things of eternal life, find it impossible to have any such idea. Such people say, "What is the internal man? Is it possible that it can be distinct from the external? What is the natural, and the rational? Are they not one? Moreover, What is the spiritual, and the celestial? Is not this a new distinction? We have heard of the spiritual, but that the celestial is something else we have not heard."
The case however is thus: They who have not previously acquired any idea on these subjects, for the reason that the cares of the world and of the body have possession of all their thought and take away all desire of knowing anything else; or because they deem it sufficient to know their doctrinal tenets as they are commonly known, and that it is of no consequence to have any further thought about the matter, saying, "We see the world, but the other life we do not see, perhaps it exists and perhaps not" - much persons put away all these subjects, for even at the first look they at heart reject them.
Nevertheless as they are such things as are contained in the internal sense of the Word, and these cannot be explained without adequate terms, and we have no terms more adequate for expressing exterior things than the term natural, for interior things than the term rational, for those things which are of truth the term spiritual, and those which are of good the term celestial, it is absolutely necessary to make use of these terms, for without terms adapted to the subject nothing can be described. ...
(Arcana Coelestia 4585)