God’s judgment upon Cain for killing his brother Abel was to be a wanderer. Cain is deathly afraid of this and says: “whoever finds me will kill me.” So God places a mark on him so that “no one who found him would kill him.” (v.14). Now who is Cain afraid of here? Supposedly the only people on earth were his mom and dad, and a few sisters. Then it says, “Cain lay with his wife.” (v.17). Where did he get a wife? Nothing was said about that, but presumably the author isn’t interested in such matters. Why? It’s because the author of chapters 3-11 was stressing the sinfulness of human beings. God created the world good, but look how his highest creation behaves—he behaves very very badly. Human beings are very sinful beginning with Adam and Eve’s disobedience, to Cain killing his brother, to the flood where God destroyed everyone but Noah and his family, to the tower of Babel. Human beings are very sinful and ungrateful for what God has done. To try to make sense of where Cain got his wife is to miss the point of these chapters. It has the feel of a story with a point, not a statement about marrying sisters. Then it says when Cain’s wife gave birth to his firstborn, Enoch, Cain was in the process of “building a city.” (v.17). If we try to make sense of this we simply cannot do it. Cain is banished from his parents and marked so that no one who finds him will kill him. He gets a wife and starts to build a city, and while doing so Enoch is born. None of this makes much sense given the whole setting. A city? Instead, maybe it should have read, “Cain was building a house.” But a whole city?
According to Donald Gown this whole scenario “seems to presuppose a different background from that provided by chapters 2-3, one in which Cain and Abel live in an already well-populated world. Furthermore, the genealogy at the end, leading to the founding of guilds of cattle-raisers, musicians, and metallurgists, seems strangely irrelevant when we realize that all the descendants of these people will be wiped out by the flood. Originally, then, the story of Cain and Abel was probably told as a self-contained narrative, without having any relationship to the stories of the garden or the flood.” [From Eden to Babel: Genesis 1-11 (pp. 62-63)].
This should surprise no one. Even the Gospels do not present the same chronology of events in the life of Jesus or stress the same things about him. The events in the life of Jesus were arranged by each of the four authors to stress certain distinct things in the life of Jesus, and very few, if any N.T. authorities think otherwise. [See almost any scholarly introduction to the Gospels for this].
But with the story of Cain we have an additional problem. If so many things in this story are inserted without the need to correct the setting, like his wife, the people he fears, and the city he is building, then when the editor/author earlier said that "Eve would become the mother of all the living"(Gen. 3:20)we can see it for what it really is. It is just a folk story with a point, like one of Jesus’ parables. John Gibson: “Genesis is essentially folk literature. The vast bulk of it consists of stories which still carry about them the marks of having been composed to entertain and to instruct ordinary folks.” “In effect we are treating this and other opening chapters of Genesis as imaginative stories, approaching them as we would a modern short story or, to use a Biblical parallel, one of our Lord’s parables.” [Genesis 1-11, (pp. 2, 11).
This view undercuts what both Jesus and Paul purportedly thought about Adam & Eve, Cain and Able too. Either they were both wrong to think of them as real historical people, or they thought these were imaginative folk-tales.
What other reasonable explanations are there?