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.

637. Clothed in sackcloth, signifies in mourning because of the non-reception of Divine good and Divine truth. This is evident from the signification of "clothed in sackcloth," as being mourning because of the vastation and desolation of Divine good and Divine truth, here because of their non-reception; for the witnesses were seen clothed in sackcloth, and they signify the Divine good, from which is every good of love and charity, and the Divine truth, from which is every truth of doctrine and faith; these appear to be in mourning when they are not received, but in joy when they are received.

[2] Likewise it is said of the sun and moon, which also signify the good of love and the truth of faith, that:

The sun became black as sackcloth of hair, and the moon became as blood (Revelation 6:12),

which signifies that every good of love was separated, and every truth of faith falsified (See above, n. 401); not that the sun in the angelic heaven, which is the Lord, ever becomes black, but that it so appears to those who receive no light from it.

[3] In ancient times, when the externals of the church consisted of mere correspondences and thence of representatives of things spiritual, mourning was represented by many things that are significative; as by sitting and lying on the ground, rolling themselves in the dust, by putting ashes on the head, rending the garments, and putting on sackcloth. "Rending the garments and putting on sackcloth" signified mourning because of the desolation of truth and good in the church, and because of the nonreception of them; for "garments" in general signified the truths of the church (See above, n. 64, 65, 195, 271, 395, 475, 476); therefore "rending the garments" signified grief because the truths of the church are hurt and as it were rent asunder by falsities; and "to be clothed in sackcloth" signifies mourning because of the deprivation of good and truth, and the consequent vastation of the church.

[4] For this reason:

When Hezekiah the king heard the words of Tartan the captain of the king of Assyria, he rent his clothes and covered himself with sackcloth, and came to the house of Jehovah; and he sent Eliakim who was over the house, and Shebna the scribe, and the elders of the priests, covered with sackcloth, to Isaiah (2 Kings 19:1, 2; Isaiah 37:1, 2).

This was done because the "king of Assyria" here signifies the perverted rational, or the rational that perverts the truths and goods of the church and destroys them by falsities; all the words of Tartan the captain of the king of Assyria, involve such things; and because the desolation and vastation of the church was seen to be imminent, to exhibit mourning and grief on this account they rent their garments and covered themselves with sackcloth.

[5] Likewise:

When Benhadad the king of Syria besieged Samaria, and there came a great famine, the king rent his clothes, and as he passed by upon the wall the people saw that, behold, sackcloth was upon his flesh within (2 Kings 6:30).

This has a similar signification as above, namely, the imminent desolation and devastation of the church; for this reason the king rent his garments and had sackcloth upon his flesh, which was a representative sign of mourning and grief.

[6] Mourning for like reasons is signified also by the following:

Jacob, when he believed that Joseph was torn to pieces, rent his clothes, and put sackcloth upon his loins, and mourned for his son many days (Genesis 37:34).

So when Ahab, by the advice of Jezebel his wife, had taken away the vineyard of Naboth, and had heard the hard words of the prophet respecting that matter, he rent his clothes and put sackcloth upon his flesh, and fasted, yea, he lay in sackcloth, and went softly (1 Kings 21:27).

The king of Nineveh also, when he heard the words of Jonah, arose up from his throne, and laid his robe from him and covered him with sackcloth, and sat upon ashes, and proclaimed a fast, and that man and beast should be covered with sackcloth (Jonah 3:5, 6, 8).

So also Daniel set his face to the Lord God, to seek by supplication and prayer in fasting, sackcloth, and ashes (Daniel 9:3).

When Abner was slain, David said to Joab and to all the people that were with him, that they should rend their clothes and gird them with sackcloth, and mourn before Abner; and David himself walked behind the bier (2 Samuel 3:31).

This makes clear that in the Jewish and Israelitish church mourning was represented by "rending the clothes and being clothed in sackcloth;" and this because grief of mind and mourning of heart, which were interior things, were represented at that time by external things, which because of their correspondences with spiritual things were significative.

[7] That the representation of mourning by sackcloth signified especially mourning because of the desolation of truth and vastation of good in the church, and also, in particular, repentance, with mourning of heart on account of evils, can be seen further from the following passages. In Isaiah:

In that day will the Lord Jehovih of hosts call to weeping and to lamenting, and to baldness, and to girding on sackcloth (Isaiah 22:12).

This chapter treats of the vastation of the church in respect to Divine truth; its mourning is described by "baldness" and by "putting on sackcloth."

[8] In Jeremiah:

The lion is gone up from the thicket, and the destroyer of nations journeyeth; he hath gone forth out of his place to make the land a waste; thy cities shall be destroyed, that there shall be no inhabitant; for this gird ye with sackcloth, lament, howl (Jeremiah 4:7, 8).

"The lion from the thicket" signifies the falsity of evil destroying the truths of the church; and "the destroyer of nations" signifies the evil of falsity destroying the good of the church; the "land that they will make a waste" signifies the church, and the "cities that shall be destroyed" signify the truths of doctrine; "to gird with sackcloth" signifies mourning on this account, therefore it is added "lament and howl."

[9] In the same:

O daughter of My people, gird thee with sackcloth and roll thee in ashes; make thee mourning for an only one, a lamentation of bitterness, for the waster shall suddenly come upon us (Jeremiah 6:26).

"Daughter of the people" means the church; "to gird herself with sackcloth and roll herself in ashes" signifies mourning because of the destruction of the good and truth of the church; the destruction of these or the vastation of the church is meant by "the waster shall suddenly come." Evidently grievous mourning and grief because of the destruction of good and truth is signified by "gird thee with sackcloth and roll thee in ashes," for it is added "make thee mourning for an only one, a lamentation of bitterness."

[10] In the same:

Howl, O Heshbon, for Ai is devastated; cry out, ye daughters of Rabbah; gird ye with sackcloth, lament, and wander among the walls; for their king is gone into exile, his priests and princes together (Jeremiah 49:3).

This is said of the sons of Ammon, who signify such as are in natural good and falsify the truths of the church; those who are such in the church are meant by "the daughters of Rabbah;" mourning because of the destruction of truth by falsifications is signified by "Gird ye with sackcloth, lament, wander among the walls," "walls" signifying truths falsified; that the truth of the church perished in consequence is signified by "their king is gone into exile," "king" signifying the truth of the church, and "to go into exile" signifying to be destroyed. That the goods of the church and all truths therefrom likewise perished, is signified by "priests and princes together," "priests" signifying the goods of the church, and "princes" the truths therefrom.

[11] In Lamentations:

The elders of the daughter of Zion sit upon the earth, they keep silence, they have cast up dust upon their head, they have girded themselves with sackcloth; the virgins of Jerusalem bend their head down to the earth (Lamentations 2:10).

"To sit upon the earth," "to keep silence," "to cast up dust upon the head," and "to make the head to bend down to the earth," were all signs representative of mourning and grief because of the vastation of the church by evils and falsities. "The elders of the daughter of Zion" signify those that are wise and intelligent in the church, and in an abstract sense wisdom and intelligence; "daughters of Zion and the virgins of Jerusalem" signify those in the church who are in the affection of good and truth, and in an abstract sense these affections themselves.

[12] In Ezekiel:

The shipmasters shall make themselves bald for thee, and gird them with sackcloth, and they shall weep over thee in bitterness of soul, with bitter lamentation (Ezekiel 27:31).

This is said of Tyre, which signifies the church in respect to the knowledges of truth and good, and therefore also the knowledges of truth and good which belong to the church; here mourning on account of the destruction of these is described. "Shipmasters" signify all who bring and communicate these knowledges; "to make bald" signifies mourning on account of the destruction of all things of intelligence; "to gird with sackcloth" signifies mourning because the ability to know truth is also destroyed. Because mourning is what is described, it is added, "they shall weep over thee in bitterness of soul, with bitter lamentation. "

[13] In the Gospels:

Woe unto thee Chorazin, woe unto thee Bethsaida, for if the mighty works had been done in Tyre and Sidon which have been done in you, they would have repented long ago in sackcloth and ashes (Matthew 11:21; Luke 10:13).

"To repent in sackcloth and ashes" means to grieve and mourn because of the nonreception of Divine truth, and because of the falsities and evils that obstruct.

[14] In Joel:

Howl as a virgin girded with sackcloth for the bridegroom of her youth; gird ye and lament, ye priests; howl, ye ministers of the altar; come, pass the night in sackcloth, ye ministers of my God, for the meal offering and the drink offering are withholden from the house of your God (Joel 1:8, 13).

Here "to be girded with sackcloth" and "to pass the night in sackcloth" signify mourning because the good and truth of the church are destroyed, for the "meal offering" signifies the good of the church, and the "drink offering" its truth.

[15] In Amos:

I will bring up sackcloth upon all loins, and baldness upon every head, and I will make it as a mourning for an only one, and its latter end as a bitter day (Amos 8:10).

"Sackcloth upon the loins" signifies mourning because the good of love is destroyed, for this is signified by the "loins;" and "baldness upon the head" signifies mourning because the understanding of truth is destroyed.

[16] In Isaiah:

Upon all the heads of Moab is baldness, every beard shaven; in its streets they have girded themselves with sackcloth; upon its roofs and in its streets he shall howl, flowing down in weeping (Isaiah 15:2, 3).

In Jeremiah:

Every head baldness, and every beard shaven; upon all hands gashes, and upon the loins sackcloth; upon all the roofs of Moab and in its streets mourning everywhere (Jeremiah 48:37, 38).

"Moab" signifies those who are in natural good and who adulterate the goods of the church; that such have no understanding of truth or knowledge [scientia] of truth is signified by "upon all the heads of Moab baldness, and every beard shaven," also by "upon its roofs and in its streets he shall howl" and "there shall be mourning;" "upon all hands gashes" signifies things falsified; mourning because of these things is signified by "to gird with sackcloth," and "to howl," and "to flow down in weeping."

[17] In Isaiah:

It shall come to pass in place of spices there shall be rottenness, and in place of a girdle tatters, and in place of braided work baldness, and in place of a robe a girding of sackcloth, in place of beauty burning; thy men shall fall by the sword, and thy might in the war (Isaiah 3:24, 25).

This is said of "the daughters of Zion," by whom the church in respect to the affections of celestial good is signified, therefore "the daughters of Zion" signify the affections of good that belong to the celestial church. The loss and dissipation of these through the pride of self-intelligence is here described by the various things with which these daughters adorn themselves; the change of these affections into opposite and unbeautiful affections is signified by "in place of spices there shall be rottenness, in place of a girdle tatters, in place of braided work baldness, in place of a robe a girding of sackcloth, and in place of beauty burning;" "rottenness" signifies the vital perishing; "in place of a girdle tatters" signifies the dissipation of perceptions of truth instead of their union; "in place of braided work baldness" signifies imbecility instead of knowledge [scientia]; "in place of beauty burning" signifies foolishness instead of intelligence, "burning" signifying insanity from the pride of self-intelligence, which is foolishness, and "beauty" signifying intelligence. That the truths of the understanding will perish by falsities, even till there is no resistance against evils, is signified by "thy men shall fall by the sword and thy might in the war," "sword" meaning falsity destroying the truth.

[18] "Sackcloth" has a similar meaning in the following passages. In Ezekiel:

All hands are relaxed, all knees go into waters, whence they shall gird themselves with sackcloth, and terror shall cover them, and upon all faces shall be shame, and upon all heads baldness (Ezekiel 7:17, 18).

In David:

I, when they were sick, made sackcloth my vesture, I afflicted my soul with hunger (Psalms 35:13).

When I wept in the fast of my soul it became to me a reproach; when I made sackcloth my garment I became a byword to them (Psalms 69:10, 11).

In Job:

I have sewed sackcloth upon my skin, and have put my horn in the dust; my face has been soiled by weeping (Job 16:15, 16).

In Isaiah:

I clothe the heavens with blackness, and I make sackcloth their covering (Isaiah 50:3).

And in David:

Thou hast turned for me my mourning into dancing, thou hast loosed my sackcloth and hast girded me with joy (Psalms 30:11).

In these passages, too, "sackcloth" signifies mourning; and "to gird sackcloth over the body instead of the vesture" signifies mourning because of the destruction of the truth of the church; and "to gird sackcloth upon the loins and upon the flesh" signifies mourning because of the destruction of the good of the church; for "the vesture" signifies the truth of the church, and "loins and flesh" signify the good of the church.

[19] That "girding with sackcloth" was merely representative and thus significative of mourning and repentance, but was not in itself mourning and repentance, is evident in Isaiah:

Is such the fast that I shall choose, the day for a man to afflict his soul, to bow down his head as a rush, and to lie down in sackcloth and ashes; wilt thou call this a fast, and the day of Jehovah's good pleasure? Is not this the fast that I choose, to loose the bonds of wickedness, to break thy bread to the hungry, and to bring the afflicted exiles to the home, and when thou seest the naked that thou cover him? (Isaiah 58:5-7)

And in Joel:

Turn ye back unto me with your whole heart, and in fasting and in weeping and in lamentation, and rend your heart and not your garments (Joel 2:12, 13).