Goodness, the plot just crackles along in this book, doesn't it? We have the first instance of biblical sex in v. 1 Adam knew Eve his wife... and the first murder just 7 verses later And Cain talked with Abel his brother: and it came to pass, when they were in the field, that Cain rose up against his brother, and slew him. Ah, sibling rivalry. I used to eat my McDonald's really slowly so I'd be the last one eating and my siblings would be jealous. Didn't work though: my dad just ate all my fries. But I digress. So why does Cain kill his brother? Well, according to Jerry, Abel's offering of the firstlings of his flock (v.4) was a blood sacrifice and his sin deserved death and could only be covered by the death of a guiltless sacrifice. Also, it was the given with the right attitude. I think he's extrapolating pretty heavily here, as the text doesn't really specify, it just says he rejected it.
God discovers the murder pretty quickly of course. Jerry jumps all over the line Thy brother's blood crieth unto me from the ground (v.10) because it shows that abortion is a sin. Of course, he is silent when God puts a mark upon Cain in verse 15 and vows to punish anyone who touches him sevenfold, because his god is anti-abortion but pro-death penalty, see.
Anyway, Cain leaves and goes to the land of Nod, which Jerry thinks is for unsaved people, which does take away some of the whimsy. He somehow finds a wife, another factoid Jerry doesn't deal with, has a son, and founds a city. Verse 18 moves us forward through the next 4 generations at a dizzying pace: Enoch, Irad, Mehujael, Methusael apparently didn't amount to much, and where they found wives gets nary a mention. Finally, Methusael has a son Lamech, who is noteworthy for having two wives: Adah and Zillah. Now, Jerry of course says that the Cananites engage in polygamy because they're the descendants of a sinner, so it will be interesting to see what he makes of other biblical polygamists as we go along.
Lamech's other accomplishment is the second murder. We don't know if he gets punished, but he does vow that if anyone who murders Cain will get a 7-fold punishment, anyone who hurts him gets a 77-fold punishment.
The chapter ends by telling us Adam and Eve have sex yet again and the result is Seth, whose son Enos finally returns humanity to the fold.
All that plot advancement in 2.5 pages. East of Eden, which is an allegory of this chapter, is what, 500+?