Jerusalem, on Mount Zion, signifies the doctrine of love to the Lord, and how it governs your life. Jerusalem first comes to our attention in 2 Samuel 5, when King David takes the city from the Jebusites and makes it his capital. In the next chapter he brings the Ark of the Covenant there, and later it is where Solomon builds the temple, and his own palace. From then on Jerusalem is the center of worship of the Israelitish church. It is the place where the Lord was presented in the temple as a baby, where He tarried to talk to the priests at age twelve, where He cleansed the temple, had the last supper, was crucified and then rose. It is a central place in both the old and new Testaments. The city was built on Mount Zion, the highest point of the mountains of Judea. A city, in the Word, represents doctrine, the organized knowledge of the truths of the church. Mountains represent love of the Lord and the consequent worship. If you put those things together, Jerusalem on Mount Zion signifies the doctrine of love to the Lord, and how it governs your life. This is why David was led to make Jerusalem the most important city of the land, and why all worship was conducted there. And this is also why Jeroboam was condemned for introducing idol worship in Samaria. In the Book of Revelation, John's vision of the city New Jerusalem descending from God is a prophecy of a new dispensation of doctrine coming from the Lord.

(Reference: Arcana Coelestia 4539, 8938; The Apocalypse Explained 365 [35-38])

557. Verse 9. (Revelation 9:9) And they had breastplates as iron breastplates, signifies the persuasions with which they gird themselves for combats, against which the truths of the rational-spiritual man prevail not. This is evident from the signification of "breastplates" (or coats of mail), as being defenses against evils and falsities in combats, but here defenses of evils and falsities against goods and truths, because this treats of those who are in the falsities of evil in opposition to truths. Here "breastplates" signify persuasions, because sensual men who are in the falsities of evil, who are here described, do not fight against truths from reason, for they do not see truths, but falsities only, and are therefore in the persuasion that falsities are truths, consequently they fight solely from the persuasion of falsity, and with them this persuasion is such that the truths brought forth by the spiritual-rational man are of no avail, for they are repelled as a sword is from a breastplate or coat of mail. So "breastplates as iron breastplates" signify persuasions against which truths are of no avail. That the persuasiveness with such is so infatuating and suffocating that the spiritual-rational is of no avail against it may be seen above (n. 544, 549, 556). Moreover, breastplates or coats of mail, cover that part of the body called the breast or thorax, and this signifies the spiritual affection of truth; also all affection is contained in the sound which comes forth from the breast with the speech. But those who are here signified by "locusts," who are such sensual men as are in falsities, have no other affection than that of the love of self, and because that affection is full of self-confidence and full of the persuasion that their falsity is truth, and because that affection is in the sound which comes forth from the breast with the speech, so the locusts appeared in "breastplates which were as iron breastplates." Moreover, "iron" signifies truth in ultimates, and likewise falsity there, and at the same time what is hard; and the persuasiveness that they have causes the falsity to be so hard that the truths opposed to it rebound, as if they were of no account or avail. Because the persuasion of sensual men who are in falsities from self-confidence is such, and with spirits is so powerful that it suffocates and extinguishes the rational of other spirits with whom they converse in the world of spirits, it is severely prohibited, and those who make use of it are sent among spirits where they are distressed even to swooning by other spirits by means of still stronger persuasions, and this until they desist.

[2] Because breastplates or coats of mail were in use in wars, and to put them on signified to gird oneself for war and thus to fight, therefore in the Word those who were girt for fighting are said to have put on coats of mail. Thus in Jeremiah:

Harness the horses, and go up, ye horsemen; and stand ye forth in helmets; furbish the spears, and put on the coats of mail (46 Jeremiah 46:4).

These words do not mean the combat of one army against another, but the combat of the spiritual-rational man against the natural man who, from knowledges [scientifica] falsely applied, fights against truths and goods. For this is said of the army of Pharaoh king of Egypt, whom the king of Babylon smote, and "Pharaoh king of Egypt" means such a natural man, and "the king of Babylon," near the Euphrates, means the spiritual-rational man, therefore "Harness the horses, go up, ye horsemen, and stand ye forth in helmets; furbish the spears, and put on the coats of mail," signifies such things as relate to the combat of the spiritual-rational man against the natural man who is in falsities; "horses" mean the things of the understanding, "chariots to which they were harnessed" the things of doctrine, "horsemen" the intelligent, "helmets" the things of reason, "spears" truths combating, and "coats of mail" force and strength in fighting and resisting. A "coat of mail" has this meaning because it girds the breast, and from the breast through the arms is all the strength in fighting and resisting.

[3] In the same:

Against Babylon let him bend, let him that bendeth bend his bow; against her he shall lift himself up in his coat of mail (Jeremiah 51:3).

Here, too, "coat of mail" stands for the power to fight and resist. In Isaiah:

He put on righteousness as a coat of mail, and the helmet of salvation upon His head (Isaiah 59:17).

This treats of the Lord, and of the subjugation of the hells by Him; and "righteousness as a coat of mail" signifies the zeal for rescuing the faithful from hell and the Divine love of saving the human race; and as it was from the zeal of Divine love and power therefrom that the Lord fought and conquered, so righteousness is called a "coat of mail;" while the "helmet of salvation" signifies Divine truth from Divine good, by means of which is salvation, for a "helmet" has a similar signification as the head, because it is worn on the head; that the "head" in reference to the Lord signifies Divine truth and Divine wisdom will be seen in what follows.