The deity tells Abram in a vision that he has nothing to fear—he'll protect Abram like a shield. That's a relief with all these foreign wars going on and all (14:1-24).
Now Abram gets a little sassy: protection is good and all, but what about kids? A family would be nice.
The deity takes Abram outside, shows him the stars, and promises him that his offspring will be as numerous as those stars (recall 13:16, where they'll be as numerous as the dust). Yowza.
The deity signals his commitment to deliver by making a covenant with Abram, and the two seal it with a ritual act.
Don't try this at home! Abram chops a bunch of animals in two and sets the two halves opposite each other.
As the sun is setting, Abram falls fast asleep.
Then a "deep and terrifying darkness descended upon him" (15:12 NRSV).
The deity foretells for Abram what will happen in the opening chapters of the biblical book of Exodus. If you've ever watched Cecil B. DeMille's The Ten Commandments, you'll know what he's talking about.
His descendants will be foreigners and immigrants in a land that does not belong to them for—count 'em—400 long years.
But God will judge the nation (namely, Egypt), and bring Abram's offspring forth with lots of wealth.
As for Abram, he'll die way before all this happens when he's good and old.
After four generations, Abram's offspring will return to Canaan.
The deity explains, "for the iniquity of the Amorites is not yet complete" (15:16 NRSV).
As soon as the sun sets, a smoking pot of fire and a torch passes between the pieces of the animals Abram has placed out.
The deity reiterates the promises to Abraham, but after 15:13-16, we know that the fulfillment of this promise is deferred until much later. A lot of suffering's going to happen first.