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.

3539. 'And put them on Jacob her younger son' means the affection for truth, that is, the life of good originating in truth. This is clear from the representation of 'Rebekah' as the Divine Truth of the Divine Rational, from the representation of 'Jacob' as the Divine Truth of the Divine Natural, and from the meaning here of 'putting on' as the communication, also the learning, of something, namely truths that clothe good, meant by 'Esau's clothes', 3537, accordingly the affection for natural truth, which affection is at this point the same as the life of good originating in truth. How these matters are to be understood may be known from what has been stated above in 3518. Yet because they are such as are completely unknown at the present day, let some explanation enabling them to be grasped be given. The subject in this chapter [in the highest sense] is the Lord and how He made His Natural Divine, and in the representative sense man's regeneration as regards his natural, see 3490.

[2] In the case of man the situation is as follows: The end in view of regeneration is that a person may be made new as regards his internal man, and so as regards the soul or spirit. But he is unable to be made new or be regenerated as regards that internal man without also being made new as regards the external man. For although a person becomes a spirit after death he nevertheless takes with him into the next life those things that belong to his external man, namely natural affections, also matters of doctrine, as well as factual knowledge; in short he takes with him everything belonging to the exterior or natural memory, see 2475-2483. Indeed these things form the groundwork on which his interiors ultimately rest. The disposition of those exterior things therefore determines what the interior become when these latter enter into the former, for within those exterior things they undergo modification. From this it is evident that a person has to be regenerated or made new not only as regards the internal or rational man but also as regards the external or natural man. Except for this there would not be any correspondence. Regarding the correspondence that exists between the internal man and the spiritual things belonging to the internal man with the external man and the natural things belonging to the external man, see 2987, 2989-2991, 3002, 3493.

[3] The state of man's regeneration is described in the representative sense in this chapter as Esau and Jacob. At this point the nature of the first stage of that state is described, that is to say, when a person is being regenerated or before he has become regenerated. In fact this state is the complete reverse of the state in which a person has become regenerate. Indeed in the former state, that is to say, when a person is being regenerated or before he has become regenerated, things of the understanding, which are those of truth, seemingly take the lead; but once he has become regenerate those of the will, which are those of good, do so. The fact that things of the understanding or of truth seemingly take the lead in the first state was represented by Jacob claiming for himself Esau's birthright - see 3325, 3336 - and then claiming his blessing, the subject under discussion here. And the fact that the state is the complete reverse of the regenerate state is represented by Jacob's impersonating Esau, that is to say, being dressed in Esau's clothes and with the skins of the kids of the she-goats. Indeed in this state rational truth has not yet been so joined to rational good, or what amounts to the same, the understanding has not been so joined to the will, as to flow and act into the natural and set in order the things that are so reversed there.

[4] This also becomes clear from much experience, in particular from this. A person is able to discern in his understanding, and from this the natural is able to know many things that are good and true, but the will is unable as yet to act in accordance with those things. Take for example the truth that love and charity are the essential thing with a human being. He is able to see and confirm this in his understanding, but until he has been regenerated he is unable to acknowledge it in his will. There are also people totally lacking in love to the Lord and in charity towards the neighbour who can well grasp this truth. The same applies to the truth that love is the very life of man, and that the nature of his life is determined by that of his love; also the truth that all delight and all pleasantness stem from love, as do all gladness and all happiness, where again the nature of the love determines that of the gladness and the happiness. A person is also able to grasp in his understanding, even though the will disagrees with it or even opposes it, the truth that the happiest life originates in love to the Lord and love towards the neighbour because the Divine itself is flowing into that life, and conversely that the unhappiest life originates in self-love and love of the world because hell is flowing into that life.

[5] Consequently the understanding, but not the will, is able to perceive the truth that love to the Lord is the life of heaven, and that mutual love is the soul from that life. In the measure therefore that a person does not think from the life of his [unregenerate] will, and does not reflect on his own life from there, he perceives that truth in his understanding; but in the measure that he does think from the life of his [unregenerate] will he does not perceive it, indeed he refuses to believe it. It may also be perfectly clear to a person in his understanding that it is into humility, if it exists in him, that the Divine is able to enter, because in that state of humility self-love and love of the world, and therefore hellish things which stand in the way, are removed. But as long as his will is not a new will, and his understanding is not united to this, no humility of heart can exist in a person. Indeed, in the measure that a person leads an evil life, that is, in the measure that his will is bent on evil, such humility cannot be there in him, and also the truth spoken of above is unclear to him and he refuses to believe it. Therefore a person may also be able to perceive in his understanding that when humility is present in someone it is not there for the sake of a love of glory in the Lord but for the sake of Divine Love, in which case the Lord is able to enter in with goodness and truth and bring blessing and happiness to that person. But to the extent that the will is consulted, this truth is obscured. And the same is so with very many other circumstances.

[6] This ability of being able to understand what good and truth is even though he does not will it has been conferred on man to enable him to be reformed and regenerated. For this reason this ability exists with evil and good alike; indeed the ability is sometimes keener with the evil. But there is this difference - with the evil no affection for truth exists for the sake of life, that is, for the sake of the good of life which originates in truth, and so they are not capable of being reformed. But with the good there does exist the affection for truth for the sake of life, that is, for the sake of the good of life, and so they are capable of being reformed. The first state in the reformation of the latter however is a state in which truth taught by doctrine seems to them to be primary, and the good of life secondary, since truth is the source of their good actions. But their second state is a state in which the good of life is primary and truth taught by doctrine secondary, since good, that is, the will for good, is the source of their good actions. And when this is the case, because the will is joined to the understanding as in a marriage, the person is regenerate. These two states are the subject in the internal sense in these incidents involving Esau and Jacob.