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.

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

9600. 'The length of one curtain shall be twenty-eight cubits' means the holiness of the truth derived from good. This is clear from the meaning of 'the length' as good, dealt with in 1613, 8898, 9487; from the meaning of 'curtain' as interior truth of faith, which belongs to the new understanding, dealt with above in 9595; and from the meaning of 'twenty-eight' as the holiness of being joined together. 'Twenty-eight' has this meaning because this number is the product of seven multiplied by four, and 'seven' means that which is holy, 433, 716, 881, 5265, 5268, and 'four' a joining together, 1686, 8877. For multiple numbers are similar in meaning to the simple ones that are their factors, 5291, 5335, 5708, 7973. From all this it is evident that 'the length of one curtain shall be twenty-eight cubits' means the holiness of the truth derived from good.