The story of Cain and Abel has been inspiring art and literature for centuries, and it’s not hard to see why – it embodies
the very human emotions of disappointment and anger, the enduring theme of family conflict, the shock of murder, the desire for forgiveness, the fear of banishment. Where Adam and Eve seem otherworldly, Cain seems all too human.
And in a sense, Swedenborg says that Cain was 
a precursor and model for modern humanity. Where those around him – including Abel – were filled with love of the Lord and acted from that love, Cain wanted to use his own mind to think about what was right and wrong, and to be led by his own thoughts. As succeeding generations turned away from the Lord and toward themselves, the states of Adam, Eve and Abel would be lost – and now, as modern humans, our only way to connect with the Lord is by using our minds to lead our hearts, the mental pattern first seen in Cain.
As discussed in detail elsewhere, Adam represents the many generations of early humans who lived in a simple, pure, innocent love of the Lord, with all their thoughts springing from that love. Eve represents the desire people eventually had to sense life as their own, which created a slight separation from the divine. The temptation of the serpent represents the desire people eventually had to use their minds, their knowledge to explore the nature of the Lord and humanity rather than simply accepting. In doing so they pulled a little farther away from the Lord, and were removed from Eden, which represents the pure love of the Lord.
Abel, according to Swedenborg, represents love and ideas that flow from love. Cain, however, represents the reverse – a state in which the mind takes primacy, with thoughts, ideas and rationality leading the state of love.
To us, this does not sound so bad. And for us, it’s not – it is in fact the path we all need to take to connect with the Lord. But it is a lower state than that of Abel, and constituted on some level a rejection of the Lord. When this became clear – in the Lord’s rejection of Cain’s gift – the thoughts and ideas of the people represented by Cain led them to reject the leadership of love, represented by the murder of Abel.
This pattern of thinking would have been devastating to other people, so the people represented by Cain had to be removed along with their ideas. But Cain still had an important use to perform.
The Lord knew what people would become – that despite his leadership they would continue to turn away from him and toward themselves. He knew that eventually that would corrupt their hearts, and evil desires would overwhelm them. And he knew what he would have to do to save them: that he would have to elevate their minds over their hearts, giving them the capacity to think about what was good and force themselves to do it, even when their hearts desired evil. In short, he knew that the simple, innocent, loving ancient people would have to become the complex, conflicted, intellectually driven people that we are today.
And he knew that when that happened, people would need knowledge – they would need a source of information about the Lord, about love, about what it is to be truly good. And the people represented by Cain, who were living from their minds but still in full knowledge of the true nature of the Lord’s love, would catalog that knowledge and preserve it so it could be passed on to future generations, and provide the knowledge that modern people would need. That’s why a mark was put on Cain to protect him, and why he was placed in a protected place “east of Eden.”
So it makes sense that we find Cain’s story so fascinating. On some level, we are Cain. We are still wandering in the land of Nod, still protected by the Lord's mark, and still trying to work our way back to Eden.
Passages from Swedenborg
Arcana Coelestia (Elliott) n. 324
324. CONTENTS
The subject is doctrinal systems which were not part of the Church, that is, which were heresies, and a new Church raised up afterwards, called Enosh.
325. The Most Ancient Church possessed faith in the Lord by way of love, but there arose out of them people who separated faith from love. Doctrine concerning faith separated from love was called Cain, while charity, which is love towards the neighbour, was referred to as Abel, verses 1, 2.
326. The worship of both of them is described, that of separated faith by Cain's gift, and that of charity by Abel's gift, verses 3, 4. Worship deriving from charity was acceptable, but not that deriving from separated faith, verses 4, 5.
327. The state of those who belonged to separated faith altered to a state that was evil. This is described as Cain's anger blazing and his face* falling, verses 5, 6.
328. It is from charity that the particular nature of faith is recognized. Also charity wishes to dwell with faith provided faith is not made the chief thing and raised up above charity, verse 7.
329. Charity was annihilated among those who separated faith and placed it above charity. This is described as Cain's killing his brother Abel, verses 8, 9.
330. Charity that had been annihilated is called 'the voice of blood'*, verse 10, erroneous doctrine 'cursed from the ground', verse 11, falsity and consequent evil 'a wanderer and fugitive in the earth', verse 12. And because they turned away from the Lord they were in danger of eternal death, verses 13, 14; but because it was faith by means of which charity would afterwards be implanted, it was utterly forbidden to violate it, which is 'putting a sign on Cain', verse 15; and to remove it from the position it held previously is the meaning of 'his dwelling towards the east of Eden', verse 16.
Apocalypse Explained 817
[3] That those who separate the knowledges of truth and good from a life in agreement with them, and believe that they may be saved by these alone, were represented by Cain, has been briefly shown in the Arcana Coelestia, where Cain and Abel are treated of, to which we shall add the following observations. It is written of Cain,
That he was the first-born of Adam, and that he tilled the ground, and brought of the fruit of the ground an offering to Jehovah; and that Abel was a shepherd of the flock, and brought of the firstlings of his flock, and of the fatness thereof; also that Jehovah had respect unto the offering of Abel, and not unto the offering of Cain, wherefore anger was kindled in Cain, and he slew his brother; that Cain, was therefore accursed, and banished from the ground, and became a vagabond and fugitive on the earth; and that Jehovah set a mark upon Cain, lest he should be slain, and appointed that whoever should slay him, should have vengeance taken on him seven-fold (Gen. iv.).
It is to be observed, that all the names of persons and places in the Word signify things and states of the church; and especially the names in the first chapters of Genesis, because the historicals in those chapters are constructed historicals, containing in them the deepest mysteries of heaven, but which are, nevertheless, most holy in the sense of the letter; because in every word there is a spiritual sense which unites the heavens with the men of the church. What those historicals involve in the spiritual sense, and what the names of the persons there signify, is explained in the Arcana Coelestia. By Cain are signified the knowledges of truth and good separate from a life in agreement with them, thus from heavenly love; and by Abel is signified heavenly love; or, what amounts to the same, by Cain is signified truth separate from good, and by Abel good conjoined to truth. And because truth is the primary thing of the church, every church being formed by truths, for from truths, or from the knowledges of truth and good, every church first commences - therefore Cain was the first-born, and was named a man (vir) of Jehovah; for by a man of Jehovah, in the Word, is signified the truth of heaven and the church; and by the ground which Cain tilled, is signified the church. The separation of truth from good is signified by the murder of Abel by Cain. For when every thing of the church is placed in truths or in knowledges, and not in goods, or in the affection of living according to truths; then good with its affections is slain. And because every thing of the church perishes when truth is separated from good; therefore Cain was banished from the ground, by which, as was said, is signified the church.
But because truths are the primary things of the church, for truths will teach men how to live, therefore a mark was set on Cain, lest any one should kill him; and it was appointed that if any one should kill him, he should be avenged seven-fold. And because truth without good is carried hither and thither, having nothing to lead it, consequently it successively wanders into falsities, and falls away from the way that leads to heaven; therefore Cain was banished from before the face of Jehovah, and became a vagabond and fugitive. The case is similar with respect to faith and charity, because faith belongs to truth, and charity to good. Thus the case is similar with respect to faith separate from charity as with what is said concerning Cain, that is, that it kills Abel its brother, which is charity, whence the church perishes. And this is signified by being banished from the ground, and becoming a vagabond and fugitive; for when faith is separated by charity then truth is successively turned into falsity, and so falls to decay.