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.

6125. 'In exchange for horses' means factual knowledge supplied from the understanding. This is clear from the meaning of 'horses' as ideas forming the understanding, dealt with in 2760-2762, 3217, 5321; and since they are spoken of in connection with Egypt, which means factual knowledge, 'horses' here are factual knowledge supplied from the understanding. But what factual knowledge supplied from the understanding is must be stated. There is an understanding part and there is a will part in the human mind, and these are situated not only in his internal man but also in his external. The human understanding is developing and growing from early childhood through to manhood, and it consists in a discernment of things gained from experience and formal knowledge, also a discernment of causes from effects as well as of consequences from a chain of causes. Thus the understanding part consists in a comprehension and perception of such things as are part of everyday life, public and private. An inflowing of light from heaven brings it into existence, and for that reason everyone's understanding is capable of being made more perfect. Understanding is given to everyone in accordance with his effort to make use of what he knows, in accordance with the life he leads, and in accordance with his individual character; no one lacks it provided he is of sound mind. A person is given it to the end that he may have freedom of choice, that is, have the freedom to choose good or evil. Unless he possesses an understanding like the one just described, he has no power of his own to make that choice; thus nothing could possibly be made his own.

[2] In addition to this it should be recognized that the understanding part of a person's mind is that which receives what is spiritual, so that it is the recipient of spiritual truth and good. For no good at all, that is, no charity, nor any truth at all, that is, any faith, can be instilled into anyone if he does not have that understanding part; but they are instilled in the measure that he does have it. This also explains why a person is not regenerated by the Lord until adult life when he does possess an understanding. Till then the good of love and the truth of faith fall like seed into utterly infertile soil. But once a person has been regenerated his understanding serves the function of enabling him to see and perceive what good is and from this what truth is. For the understanding converts things belonging to the superior light of heaven into those belonging to the inferior light of the natural world, as a consequence of which the former are then seen within the latter in the same way as a person's inner affections are seen in his face when it lacks all pretence. And because the understanding serves that function, many places in the Word where the spiritual side of the Church is referred to refer also to its power of understanding, a matter which will in the Lord's Divine mercy be dealt with elsewhere.

[3] From all this one may now see what is meant by factual knowledge supplied from the understanding, namely known facts which lend support to the things a person grasps and perceives with his understanding, whether those things are bad or good. Such facts are what are meant in the Word by 'horses from Egypt', as in Isaiah,

Woe to those who go down into Egypt for help, and rely on horses and trust in chariots because they are many, and on horsemen because they are extremely strong, but do not look to the Holy One of Israel and do not seek Jehovah. For Egypt is man (homo), not God; and his horses are flesh, not spirit. Isaiah 31:1, 3.

'Horses from Egypt' stands for factual knowledge supplied from a perverted understanding.

[4] In Ezekiel,

He rebelled against him by sending his ambassadors to Egypt, that ha might give him horses and many people. Will he prosper? Will he who does this be rescued? Ezekiel 17:15.

'Horses from Egypt' again stands for factual knowledge supplied from a perverted understanding, which knowledge is resorted to in matters of faith, though there is no belief in the Word, that is, in the Lord, apart from what that knowledge provides. Thus no belief ever comes to exist, for within a perverted understanding a negative attitude reigns.

[5] The destruction which such factual knowledge underwent is represented by the drowning of Pharaoh's horses and chariots in the Sea Suph; and since that knowledge is meant by 'horses' and false matters of doctrine by 'chariots', his horses and chariots are mentioned so many times in the description of that event, see Exodus 14:17-18, 27, 26, 28. And the Song of Moses and Miriam consequently contains these words,

Pharaoh's horse went, also his chariot, also his horsemen, into the sea; but Jehovah made the waters of the sea come back over them. Sing to Jehovah, for He has highly exalted Himself; He has thrown the horse and its rider into the sea. Exodus 15:19, 21.

[6] Similar factual knowledge is also meant by the things required before-hand for a king over Israel, in Moses,

If they desire a king, from among their brothers shall a king be set over them. Only let him not multiply horses for himself nor lead the people back into Egypt in order to multiply horses. Deuteronomy 17:15-16.

'A king' represented the Lord as regards Divine Truth, 1672, 1728, 2015, 2069, 3009, 3670, 4575, 4581, 4789, 4966, 5044, 5068, thus as regards intelligence since this comes, when it is genuine, from Divine Truth. The need for intelligence to be acquired through the Word, which is Divine Truth, and not through factual knowledge taken from one's own understanding is meant by the injunction that the king should not multiply horses or lead the people back into Egypt in order to multiply horses.