'A wall,' as in Revelation 21, signifies the divine truth proceeding from the Lord, and so, the truth of faith from the good of charity. 'A wall' signifies truth in outer extremes.

(References: Apocalypse Explained 21; Apocalypse Revealed 132)

21. In Asia, signifies those who are in the light of intelligence. This can be seen by a spiritual idea only, such as angels have, concerning the regions of this earth. When Asia is named, angels perceive the south; when Europe is named, the north; and when Africa, the east; and as by the "south" is signified the clear light of intelligence, so that light is signified by "Asia." This perception has been granted also to me, as often as I have been in the spiritual idea and have thought of Asia. Such is the spiritual idea of Asia, because the church was there in ancient times, and then extended over many regions there; therefore, those who are in heaven from that country are in the light of intelligence. For this reason, when Asia is thought of, a light like that which is in the south of heaven flows in. (That in ancient times, and also in the most ancient, the church was in Asia, extending through many kingdoms there, see the quotations from the Arcana Coelestia in the little work on The New Jerusalem and its Heavenly Doctrine 247; and that the "south" signifies the light of intelligence, see in the work on Heaven and Hell 141-153, where the Four Quarters in Heaven are treated of.) By "Asia," however, the inhabitants of Asia are not here meant, but all, wheresoever they are, who are in the spiritual light of intelligence, or, what is the same, who are in truths from good; for those who are in truths from good are in the spiritual light of intelligence; and all such constitute the Lord's church.

(That the Lord's church exists also among the Gentiles, although specifically where the Lord is known and the Word is read, see in the work on Heaven and Hell 318-328; and on The New Jerusalem and its Heavenly Doctrine 244, 246.)