'Skins' or 'hides' signify external things, because the hide is the outermost organ of an animal where its interiors extend, the same as with a person's dermis or skin. 'Skin' corresponds to truth or to falsity in the extremes. See Arcana Coelestia 1835, 10036, and Apocalypse Explained 386. 'Skin,' as in Job 19:26, means the natural degree a person has with him after death.

In Exodus 22:27, this signifies things that are relatively external. (Arcana Coelestia 9215)

In Exodus 34:29, this signifies the internal of the Word shining from the external. (Arcana Coelestia 10691)

In Job 19:20, this signifies being not entirely in falsities. (Apocalypse Explained 556[11])

In Jeremiah 13:23, this signifies that evil cannot change its nature. (Apocalypse Explained 780[5])

In Genesis 3:21, this signifies that the Lord instructed them in spiritual and natural good. (Arcana Coelestia 292)

In Genesis 27:16, this signifies the external truths of domestic good. (Arcana Coelestia 3540)

5774. 'And each one loaded his ass, and they returned to the city' means that truths were brought back up from sensory impressions to known facts. This is clear from the meaning of an ass' as factual knowledge, dealt with in 5492, and of 'loading' it as bringing back up from sensory impressions since 'causing one's pouch to come down to the earth' means bringing the contents of the natural down to the level of sensory impressions, 5767 (raising 'the pouch' up from these is what 'loading' implies here); and from the meaning of 'the city' as truth present in doctrine, dealt with in 402, 2449, 2947, 3216.

[2] A brief explanation must be given of what bringing truths back up from sensory impressions to known facts is. Sensory impressions are one thing, known facts another, and truths yet another; they are consecutive to one another, for sensory impressions give rise to factual knowledge, and factual knowledge leads on to truths. Images that come in through the senses are stored in a person's memory; then he uses those images either to deduce a fact or to gain a perception of some fact he is learning about. After that he uses these facts either to deduce certain truths or to gain a perception of some truth he is learning about. This is the way everyone develops onwards from childhood. While he is a child a person's thought and grasp of things relies on sensory impressions; as he grows older his thought and grasp of things relies on factual knowledge, and after that on truths. This is the path leading to the power of judgement a person enters into as he matures.

[3] From this one may see that sensory impressions, known facts, and truths are distinct and separate. Indeed the three remain so distinct that sometimes a person's attention is fixed on sensory impressions, as happens when he gives thought only to what impinges on his senses; sometimes his attention is fixed on facts, as happens when he rises above sensory impressions and thinks more deeply; and at other times his attention is fixed on truths which have been inferred from facts, as happens when he thinks more deeply still. Anyone who stops to reflect can know these things from what is present within himself. In addition a person can bring truths down into known facts and see those truths within them, even as he can bring facts down into sensory impressions and consider them within these. And he can do the opposite. From all this one may see what is meant by bringing the contents of the natural down to the level of sensory impressions, and bringing truths back up from sensory impressions to known facts.