The number "four" in the Bible represents things being linked together or joined. This is partly because four is two times two, and two represents the ultimate linking between our desire to be good and our understanding of truth. We can also see this in the fact that most buildings are rectangular, with the four sides linking together to make a whole. We also divide directions into four -- north, east, south and west -- and talk about the "four corners" of something meaning all of it. So our special thinking naturally looks at four sides as linking together into a whole.

(Reference: Apocalypse Explained 417; Arcana Coelestia 1686, 9103, 9601, 9767, 9864)

6313. When a person is raised up to more internal levels he passes from the dull light on the level of the senses to a quite gentle light. At the same time he is removed from the inflow of what is disgraceful or foul and is brought closer to what is just and fair, because he is brought closer to the angels present with him, thus closer to the light of heaven. This raising up from the level of the senses was well-known to the ancients, and also to gentiles; and that is why the sages among them have said that when the mind is removed from the sensory level, it comes into inner light and at the same time into a state filled with peace and into a kind of heavenly bliss. From this they also made deductions about the immortality of the mind. A person can be raised to even more internal levels; and the further he goes, the clearer is the light that he comes into. At length he is raised up into the light of heaven, a light that is nothing else than wisdom and intelligence from the Lord. With the three heavens nothing else marks off one from another than the internal levels to which it is raised, and so also the degree of light that it possesses. Because it exists at the inmost levels the third heaven is in the greatest light, thus in wisdom far surpassing the wisdom of lower heavens.