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.

4495. 'It happened on the third day' means that which is continuous even to the end. This is clear from the meaning of 'the third day' as that which is complete from beginning to end, dealt with in 2788, and so also as that which is continuous. People who suppose that the historical events described in the Word are no more than the facts of earthly history and are holy only because they appear in a sacred book are scarcely able to believe that 'the third day' has that meaning. But, as shown in preceding explanations, it is not only the actual historical narratives that include spiritual and celestial things which are not plainly visible in the letter, but also every word and every number too. The truth of this will in the Lord's Divine mercy be seen far more clearly in the prophetical sections which in the sense of the letter do not hold the mind to the sequence of events in the way that the historical sections do. But anyone who looks carefully into the interior contents of the Word comes to see that the number three, like the number seven, and also the number twelve, holds some arcanum. And if these numbers hold such it follows that every other number in the Word holds the same, for the Word is holy in every part.

[2] Sometimes, when I have been talking to angels, I have seen in front of me what looked like numbers written, as if on a sheet of paper, in broad daylight, and I have realized that the spiritual entities about which the angels spoke pass into numbers like these. From this experience I have also been given to know that each number in the Word contains some arcanum. This may be seen plainly from the following in John,

He measured the wall of the holy Jerusalem, a hundred and forty-four cubits, which is the measure of a man, that is, of an angel. Revelation 21:17.

And elsewhere,

Let him who has intelligence reckon the number of the beast, for it is the number of a man, that is, its number is six hundred and sixty-six. Revelation 13:18.

It is evident that the first of these numbers, namely a hundred and forty-four, is the product of twelve times twelve, and that the number six hundred and sixty-six is a product of that involving three or six; but what degree of holiness is implied by them may be seen from the holiness associated with the number twelve, concerning which number see 577, 2089, 2129 (end), 2130 (end), 3272, 3858, 3913; and concerning the holiness associated with the number three, 720, 901, 1825, 2788, 4010.

[3] Because the number three meant that which is complete even to the end, and so an entire period, whether long or short, it was therefore adopted in the representative Church and used whenever such a meaning needed to be conveyed. It is also used in the same way in the Word, in which every detail carries a spiritual meaning, as may be seen from the following places:

They were to go a three days' journey and to offer sacrifice. Exodus 3:18; 5:3.

They were to be ready on the third day, for on the third day Jehovah would come down onto Mount Sinai. Exodus 19:11, 15-16, 18.

Nothing from the flesh of a sacrifice was to be left until the third day. Leviticus 7:16-18; 19:6-7.

The water of separation was to be sprinkled over the unclean person on the third day and on the seventh day. Numbers 19:11-end.

Those who touched one killed in war were to be cleansed on the third day and on the seventh day. Numbers 31:19-25.

[4] Joshua commanded the people that within three days they would be crossing the Jordan. Joshua 1:11; 3:2.

Jehovah called Samuel three times, and three times Samuel ran to Eli and the third time Eli understood that Jehovah was calling Samuel. 1 Samuel 3:1-8.

Jonathan told David to hide in the field until the third evening. And Jonathan sent to him on the third day from then, and revealed his father's intention. Jonathan at that point fired three arrows to the side of the stone. And after that David bowed down to the ground three times before Jonathan. 1 Samuel 20:5, 12, 19-20, 35-36, 41.

Three things were set before David, of which he was to choose one - either the coming of famine for seven years, or his fleeing before his enemies for three months, or the existence of pestilence in the land for three days. 2 Samuel 24:11-13.

[5] Rehoboam told the assembly of Israel which asked for relief from his father's yoke that they should go away for three days and then return And they came to Rehoboam on the third day, as the king said, Return to me on the third day. 1 Kings 12:5, 12.

Elijah stretched himself over the widow's son three times. 1 Kings 17:21.

Elijah told them to pour water over the burnt offering and the wood a third time and they did so a third time. 1 Kings 18:34.

Jonah was in the stomach of the monster for three days and three nights Jonah 1:17; Matthew 12:40.

The Lord talked of someone who planted a vineyard and sent servants three times, and after that his son. Mark 12:2, 4-6, Luke 20:12-13.

Of Peter, He said that he was to deny Him three times. Matthew 26:34, John 13:38.

He said to Peter three times, Do you love Me? John 21:15-17.

[6] From these and many other places in the Word it becomes clear that the number three holds an arcanum within it, and that for this reason this number was adopted within the ancient Churches as a meaningful sign. It is evident that it means the entire period of a Church and of things within a Church, whether long or short, and therefore that which is complete and also that which is continuous even to the end, as is plain in Hosea,

Jehovah will revive us after two days, on the third day He will raise us up, and we shall live before Him. Hosea 6:2.