The chapter
Simply Two brothers bring offerings, one is accepted and one is not, and the one who was not kills the other. He is questioned, cursed, and then marked for protection. The chapter ends with his descendants and with a third son born to Adam.
Context Something worth checking rather than assuming: THE WORD SIN FIRST APPEARS IN THE BIBLE HERE, at verse 7, not in the garden. The whole of chapters 1 to 3 does not use it. Whatever chapter 3 is, the book gives the word its first outing in a warning spoken to Cain before he kills.
Verses 1-16
Simply Cain works the ground and Abel keeps sheep. Both bring offerings; Abel's is respected and Cain's is not. Cain is warned, kills his brother in a field, and answers a question with a question. He is driven out, protests, and is given a mark.
Context The text does not say why one offering was respected and the other was not, and this file does not supply a reason, because every reason on offer is read into the silence rather than out of the verse. Two things it does say are easy to reverse: the warning at verse 7 comes BEFORE the killing, and the mark at verse 15 is protection and not punishment, given so that nobody would kill him.
Verses 17-26
Simply Cain's line is listed, and with it the first city, the first tent-dwellers with livestock, the first musicians, and the first metalworker. Then Lamech boasts of a killing. Then Seth is born, and men begin to call on the name of the Lord.
Context The list is not a condemnation of what it lists: cities, herding, music and metal are simply recorded as beginning here. What the chapter does track is the arithmetic of vengeance, from sevenfold at verse 15 to seventy-seven at verse 24, and the same numbers come back in Matthew 18 when Peter asks how often he should forgive.