In the third chapter of the Book of Jonah, Jonah finally reaches Nineveh, and starts preaching repentance and reformation to the people there. And... they listen! Even the King of Assyria listens!

The inner meaning of the story is pretty close to the surface here, and there's important symbolism. Swedenborg summarizes the chapter's meaning in this one sentence:

"The nations, hearing from the Word of God about their sins, and that they would perish, were converted after repenting, and were heard by the Lord, and saved." (The Inner Meaning of the Prophets and Psalms 213)

Rev. George McCurdy, in his exegesis of this chapter, offers this summary:

The great city of Nineveh has many spiritual representations. The world saw Nineveh as a mighty nation, but in the eyes of the Lord, it represented the shallowness and weakness (death) of false doctrines, contrived beliefs confirmed by the proprium (self love), the fallacies of the senses, and the unenlightened understanding that spawns spiritual ignorance.

The Lord’s mercy and love for all prompted Him not only to send His message to Nineveh, but to ensure that it would be preserved for eternity. Jonah’s call to "arise and go" preach to Nineveh is a call for spiritual renewal. It is a call for repentance. The fasting, sackcloth, and ashes symbolize a call to be aware that "where there is no truth, there is no church."

Where the Word is closed, and not loved, there is a loss of conjunction with the Divine resources. The fasting of man and beast symbolizes a need for the spiritual and natural appetites to come to the Lord for that "bread which comes down from heaven." The Ninevites giving up their natural food and drink represents their turning away from "as-of-self" concepts and reminds all who read and hear the Word of the Lord to rely on heavenly manna.

"Why do you spend money for what is not bread, and your wages for what does not satisfy? Listen carefully to Me and eat what is good, and let your soul delight itself in abundance…" (Isaiah 55:2)

The king sitting in ashes and mourning represents a sorrowful attitude toward "the remains of the fire of self-love." Repentance involves self-examination, making oneself guilty for the sins and evils committed, asking the Lord for His help, and desiring to attain a new life.

As we mull over this concept, think about the Lord’s preaching on earth. As He went about His mission, He often used these words: "You have heard it said of old… but I say unto you…" Putting aside human traditions and taking on the Lord’s teachings is an ongoing effort. Jonah was told to preach the words of the Lord. He was not to make things up from his memory. He was to be a true and faithful prophet of the Lord’s ways.

Here's a link to an interesting (audio) sermon on this chapter, by Rev. Todd Beiswenger.

Rev. Martin Pennington suggests two explanatory passages from Swedenborg's theological writings:

"Forty days means a period of temptation combats or severe change." (Arcana Coelestia 730)

"A fast represents those who are in a state of unhappiness when good is no longer joined to the truths." (Arcana Coelestia 9182[10])

Other references of interest listed by Rev. McCurdy include:

"As ‘forty’ signified what is full or complete… forty signifies what is complete in respect to instruction and influx… for this reason it was said by Jonah to the Ninevites that ‘the city would be overthrown after forty days" (Jonah 3:4) (Arcana Coelestia 9437[2])

"By being clothed in sackcloth is signified mourning on account of the vastated truth in the church; for garments signify truths; and therefore, to be clothed in sackcloth, which is not a garment, signifies mourning that there is no truth; and where there is no truth, there is no church." Jonah 3:5-6 is cited. (Apocalypse Revealed 492)

"…the rite of putting sackcloth on the loins to testify…mourning may be seen from the historic and prophetic parts of the Word, as in… Jonah 3:5-8… for a sign representative of mourning over the evil on account of which Nineveh was to perish; thus over destroyed good." (Arcana Coelestia 4779[2])

"From the signification of garments it is also manifest why they rent their garments, when any one spoke against the Divine truth of the Word… and why, on account of transgressions against Divine truths, they put off their garments, and put on sackcloth." Jonah 3:5, 6, and 8 are cited. (Apocalypse Revealed 166)

"That ‘ashes’ denote falsity, may be confirmed from passages where another word for ‘ashes (cinis)’ is used, for these ashes have a like origin…" Jonah 3:6 is cited. (Arcana Coelestia 7520)

"…by ‘ashes’ in the opposite sense, namely, what is condemned that remains after the burning from the fire of self love. This is signified by ‘the ashes’ which they carried on the head, and in which they rolled themselves when bewailing their sins." Jonah 3:6 is cited. (Arcana Coelestia 9723)

"In the spiritual sense by kings those who are in truths are signified, by the great ones those who are in goods, by the rich those that are in the knowledge of good, by the mighty they that are in erudition, by servants they that are in such things from others, and thus from memory, and by freemen they that are in such things from themselves…" Jonah 3:7 is cited. (Apocalypse Revealed 337)

"The interior good and also the interior evil…are signified by ‘man,’ are those which are of the intention or end, for the intention or end is the inmost of man; but the exterior good and also the exterior evil which are signified by ‘beast,’ are those which are of the thought, and of the consequent action when nothing stands in the way…By ‘beast,’…in respect to the external or natural man, a man is nothing else than a beast, for he takes delight in the like cupidities and pleasures, as also in the like appetites and sense…Therefore… from a holy rite it was commanded by the king of Nineveh, that both man and beast were to fast, and were to be covered with sackcloth (Jonah 3:7, 8)." (Arcana Coelestia 7523)

"… in the spiritual world a man’s affections appear at a distance like beasts… and beasts, viewed in themselves, are nothing but forms of natural affections… By man and beasts together is signified man as to spiritual and natural affection, in the following passages… Jonah 3:7, 8…" (Apocalypse Revealed 567)

"Here ‘webs’ and ‘garments’ are predicated of things of the understanding, that is, of the thought; ‘iniquity’ and ‘violence,’ of things of the will, that is, of works. In Jonah 3:8… the ‘evil way’ is predicated of falsities, which are of the understanding; and ‘violence,’ which are of the will." (Arcana Coelestia 623[2])

"…the ‘wrath of anger’ is attributed to Jehovah, and consequently ‘repentance.’" (Arcana Coelestia 588[2])

"…the Word is such in the sense of the letter, it may be evident that it cannot be understood without doctrine. But let examples illustrate this. It is said that Jehovah repenteth (Jonah 3:9; 4:2), and it is also said that Jehovah repenteth not (Num. 23:19…): without doctrine these statements do not agree." (Teachings Regarding the Sacred Scripture 51)

"In these passages (Jonah 3:9,10) Jehovah is said to have ‘repented,’ when yet it cannot be that He repents, because He knows all things before He does them; from which it is evident that by ‘repenting’ is signified mercy." (Arcana Coelestia 10441[2-4])

Finally, here's a link to Rev. McCurdy's study guide for the Book of Jonah, which is available for free as a .pdf, for your use.

7973. 'Around six hundred thousand men on foot' means all aspects of the truth and good of faith in their entirety. This is clear from the meaning of the number 'six hundred thousand' as all aspects of faith in their entirety, for this number is a multiple of six and also of twelve, and 'twelve' means all aspects of faith and charity, 577, 2089, 2129 (end), 2130 (end), 3272, 3858, 3913. This is why Jacob's sons were twelve in number, why their descendants were divided into the same number of tribes, and also why the Lord chose twelve disciples, that is to say, in order that they might represent all aspects of faith and charity. Regarding the tribes, see 3858, 3862, 3926, 3979, 4060, 6335, 6737, 6640, 7876, 7891; and regarding the disciples, 3354, 3488, 5858 (end), 6397.

[2] At this point 'six hundred thousand' has a similar meaning because a larger or smaller number that is a multiple or a factor carries a meaning similar to that of the simple numbers that are being multiplied or divided, 5291, 5335, 5708. This is plainly evident from the number twelve. Whether this is divided into six or multiplied into seventy-two, 144 (which is twelve twelves), 12000, or 144000, the meaning is similar, as with 144000 in John,

I heard the number of the sealed, a hundred and forty-four thousand, sealed out of every tribe of Israel - out of each tribe twelve thousand. Revelation 7:4-5 and following verses.

Here 'the children of Israel' is not used to mean the children of Israel, 'tribes' the tribes, or 'the number' a number, but to mean the kinds of things contained in the internal sense, namely all aspects of faith and charity. Each tribe in particular accordingly means one kind or one group, in keeping with the explanations at Genesis 29, 30.

[3] Similarly with the following in the same author,

Behold, a Lamb standing on Mount Zion, and with Him 144000, having His Father's name written on their foreheads. They were singing a new song before the throne, and no one could learn the song except 144000 bought from the earth. These are the ones who follow the Lamb wherever He goes. These were bought from men (homo), being the first fruits to God and the Lamb. Revelation 14:1, 3-4.

From this description it is evident that those governed by charity are meant by 144000. It is also evident that the sole purpose of this number is to indicate the state and its essential nature. That number is similar to twelve in what it indicates, for it is the product of 12000 and it multiplied.

[4] It is similar with the smaller number 144, Which is twelve times twelve, in the same author,

He measured the wall of the holy Jerusalem coming down from God out of heaven, 144 cubits, which is the measure of a man (homo), that is, of an angel. Revelation 21:2, 17.

'The wall of the holy Jerusalem' is not in the spiritual sense a wall; instead it is the truth of faith defending things of the Church, see 6419; and this also is why it is said to have been '144 cubits'. It is plainly evident that such must be meant, since it says 'it is the measure of a man, that is, of an angel'. 'Man' and 'angel' mean every aspect of the truth and good of faith.

[5] The same is also evident from the twelve precious stones that the foundation of the wall consisted of, and from the twelve gates, each of which was a pearl, Revelation 21:19-21. For by 'precious stones' truths of faith that spring from the good of charity are meant, 643, 3720, 6426, and similarly by 'gate' and also by 'pearl'. From this it is now clear that a smaller or larger number carries a meaning similar to the simple number that is divided or multiplied. As regards the fact that all numbers in the Word mean spiritual things, see 481, 487, 575, 647, 648, 755, 813, 1963, 1988, 2075, 2252, 3252, 4164, 4495, 4670, 5265.

[6] From these considerations one may now see that the number 'six hundred thousand' men going out of Egypt also means such things. But scarcely anyone is able to believe that such are meant by this number because it refers to a historical event; and any historical event fixes the mind all the time on the external sense and draws it away from the internal sense. Nevertheless that number too means such spiritual things, for there is not a part of a word, not even indeed one jot or one tittle in the Word, that is not in itself holy, because it holds what is holy within it. Anyone at all can see that there is nothing holy about a merely historical event.