The following is Chapter 5 of Emanuel Swedenborg’s book Heaven and Hell, taken from Sacred-Texts.com because their website is not mobile friendly. So I copied the preface here which will be read and discussed during our family study time this coming Saturday. Information about the Chinese translation of this book can be seen here.
THERE ARE THREE HEAVENS. There are three heavens, entirely distinct from each other, an inmost or third, a middle or second, and an outmost or first. These have a like order and relation to each other as the highest part of man, or his head, the middle part, or body, and the lowest, or feet; or as the upper, the middle, and the lower stories of a house. In the same order is the Divine that goes forth and descends from the Lord; consequently heaven, from the necessity of order, is threefold.
The interiors of man, which belong to his mind and disposition, are also in like order. He has an inmost, a middle, and an outmost part; for when man was created all things of Divine order were brought together in him, so that he became Divine order in form, and consequently a heaven in miniature. 30-1 For this reason also man, as regards his interiors, has communication with the heavens and comes after death among the angels, either among those of the inmost, or of the middle, or of the outmost heaven, in accordance with his reception of Divine good and truth from the Lord during his life in the world.
The Divine that flows in from the Lord and is received in the third or inmost heaven is called celestial, and in consequence the angels there are called celestial angels; the Divine that flows in from the Lord and is received in the second or middle heaven is called spiritual, and in consequence the angels there are called spiritual angels; while the Divine that flows in from the Lord and is received in the outmost or first heaven is called natural; but as the natural of that heaven is not like the natural of the world, but has the spiritual and the celestial within it, that heaven is called the spiritual-natural and the celestial-natural, and in consequence the angels there are called spiritual-natural and celestial-natural. 31-1 Those who receive influx from the middle or second heaven, which is the spiritual heaven, are called spiritual-natural; and those who receive influx from the third or inmost heaven, which is the celestial heaven, are called celestial-natural. The spiritual-natural angels and the celestial-natural angels are distinct from each other; nevertheless they constitute one heaven, because they are in one degree.
In each heaven there is an internal and an external; those in the internal are called there internal angels, while those in the external are called external angels. The internal and the external in the heavens, or in each heaven, hold the same relation as the voluntary and intellectual in man-the internal corresponding to the voluntary, and the external to the intellectual. Everything voluntary has its intellectual; one cannot exist without the other. The voluntary may be compared to a flame and the intellectual to the light therefrom.
Let it be clearly understood that with the angels it is the interiors that cause them to be in one heaven or another; for as their interiors are more open to the Lord they are in a more interior heaven. There are three degrees of interiors in each angel and spirit, and also in man. Those in whom the third degree is opened are in the inmost heaven. Those in whom the second degree is opened, or only the first, are in the middle or in the outmost heaven. The interiors are opened by reception of Divine good and Divine truth. Those who are affected by Divine truths and admit them at once into the life, thus into the will and into action therefrom, are in the inmost or third heaven, and have their place there in accordance with their reception of good from affection for truth. Those who do not admit truths at once into the will but into the memory, and thence into the understanding, and from the understanding will and do them, are in the middle or second heaven. But those who live morally and who believe in a Divine, and who care very little about being taught, are in the outmost or first heaven. 33-1 From this it is clear that the states of the interiors are what make heaven, and that heaven is within everyone, and not outside of him; as the Lord teaches when He says: The kingdom of God cometh not with observation, neither shall they say, Lo here, or Lo there; for behold the kingdom of God ye have within you (Luke 17:20, 21).
Furthermore, all perfection increases towards interiors and decreases towards exteriors, since interiors are nearer to the Divine, and are in themselves pure, while exteriors are more remote from the Divine and are in themselves grosser. 34-1 Intelligence, wisdom, love, everything good and the resulting happiness, are what constitute angelic perfection; but not happiness apart from these, for such happiness is external and not internal. Because in the angels of the inmost heaven the interiors have been opened in the third degree their perfection immeasurably surpasses the perfection of angels in the middle heaven, whose interiors have been opened in the second degree. So the perfection of these angels exceeds in like measure the perfection of angels of the outmost heaven.
Because of this distinction an angel of one heaven cannot go among the angels of another heaven, that is, no one can ascend from a lower heaven and no one can descend from a higher heaven. One ascending from a lower heaven is seized with a distress even to anguish, and is unable to see those who are there, still less to talk with them; while one descending from a higher heaven is deprived of his wisdom, stammers in his speech, and is in despair. There were some from the outmost heaven who had not yet been taught that the interiors of angels are what constitute heaven, and who believed that they might come into a higher heavenly happiness by simply gaining access to a heaven where higher angels are. These were permitted to enter among such angels. But when they were there they could see no one, however much they searched, although there was a great multitude present; for the interiors of the newcomers not having been opened in the same degree as the interiors of the angels there, their sight was not so opened. Presently they were seized with such anguish of heart that they scarcely knew whether they were alive or not. Therefore they hastily betook themselves to the heaven from which they came, glad to get back among their like, and pledging themselves that they would no longer covet higher things than were in agreement with their life. Again, I have seen some let down from a higher heaven; and these were deprived of their wisdom until they no longer knew what their own heaven was. It is otherwise when, as is often done, angels are raised up by the Lord out of a lower heaven into a higher that they may behold its glory; for then they are prepared beforehand, and are encompassed by intermediate angels, through whom they have communication with those they come among. From all this it is plain that the three heavens are entirely distinct from each other.
Those, however, who are in the same heaven can affiliate with any who are there; but the delights of such affiliation are measured by the kinships of good they have come into; of which more will be said in the following chapters.
But although the heavens are so distinct that there can be no companionship between the angels of one heaven and the angels of another, still the Lord joins all the heavens together by both direct and mediate influx-direct from Himself into all the heavens, and mediate from one heaven into another. 37-1 He thus makes the three heavens to be one, and all to be in such connection from the First to the Last that nothing unconnected is possible. Whatever is not connected through intermediates with the First can have no permanent existence, but is dissipated and becomes nothing. 37-2.
Only he who knows how degrees are related to Divine order can comprehend how the heavens are distinct, or even what is meant by the internal and the external man. Most men in the world have no other idea of what is interior and what is exterior, or of what is higher and what is lower, than as something continuous, or coherent by continuity, from purer to grosser. But the relation of what is interior to what is exterior is discrete, not continuous. Degrees are of two kinds, those that are continuous and those that are not. Continuous degrees are related like the degrees of the waning of a light from its bright blaze to darkness, or like the degrees of the decrease of vision from objects in the light to those in the shade, or like degrees of purity in the atmosphere from bottom to top. These degrees are determined by distance.  On the other hand, degrees that are not continuous, but discrete, are distinguished like prior and posterior, like cause and effect, and like what produces and what is produced. Whoever looks into the matter will see that in each thing and all things in the whole world, whatever they are, there are such degrees of producing and compounding, that is, from one a second, and from that a third, and so on.  Until one has acquired for himself a perception of these degrees he cannot possibly understand the differences between the heavens, nor between the interior and exterior faculties of man, nor the differences between the spiritual world and the natural world, nor between the spirit of man and his body. So neither can he understand the nature and source of correspondences and representations, or the nature of influx. Sensual men do not apprehend these differences, for they make increase and decrease, even according to these degrees, to be continuous, and are therefore unable to conceive of what is spiritual otherwise than as a purer natural. And in consequence they remain outside of and a great way off from intelligence. 38-1
Finally, a certain arcanum respecting the angels of the three heavens, which has not hitherto come into any one’s mind, because degrees have not been understood, may be related. In every angel and also in every man there is an inmost or highest degree, or an inmost or highest something, into which the Divine of the Lord primarily or proximately flows, and from which it disposes the other interiors in him that follow in accordance with the degrees of order. This inmost or highest degree may be called the entrance of the Lord to the angel or man, and His veriest dwelling-place in them. It is by virtue of this inmost or highest that a man is a man, and is distinguished from irrational animals, for these do not have it. From this it is that man, unlike the animals, is capable, in respect to all his interiors which pertain to his mind and disposition, of being raised up by the Lord to Himself, of believing in the Lord, of being moved by love to the Lord, and thereby beholding Him, and of receiving intelligence and wisdom, and speaking from reason. Also, it is by virtue of this that he lives to eternity. But what is arranged and provided by the Lord in this inmost does not distinctly flow into the perception of any angel, because it is above his thought and transcends his wisdom.
These now are the general truths respecting the three heavens; but in what follows each heaven will be particularly treated of.