2 Samuel Chapter 12 Summary

God sends the prophet Nathan to David to tell him a short story.
Nathan tells David that there was once a poor man who had a little ewe lamb that he cared for. It was his favorite pet, and he fed it and treated it kindly as though it were a daughter to him.
But one day, a traveler was visiting a local rich man, and, instead of killing one of his own sheep, the rich man took the poor man's lamb and fed it to his guest.
David angrily says that the rich man should've been killed for doing such an evil thing. He should, at least, be forced to pay back the poor man four-fold for stealing his sheep.
Nathan says, "Dude—don't you get it? You are the rich man."

Nathan further clarifies God's message for David and his punishment for this terrible sin. God raised David up to these heights, made him king, gave him plenty of wives and wealth. But greedy for more, David stole and coveted another man's wife, and murdered that man to boot. Yikes.
As punishment, God says that David's house will always be at war, and that David's "neighbor" (actually, it turns out to be a family member) will sleep with David's own wives in the plain sight of Israel. Double yikes.
David admits he's sinned against and before God. Nathan says that's good, and David won't die or lose God's favor forever.
But he needs to pay the penalty. Dun dun dun.

So. God gives the kid David had with Bathsheba some sort of illness—and the boy looks like he's on his way to dying.
David begs God not to let his son die. He fasts and prays.
The elders try to pull David out of his state of fasting and repenting, but David refuses to get up.
Soon enough, the child dies. David sees the servants whispering about it and realizes what's happened. The servants confirm it.
So, David gets up, washes, anoints himself, worships God, and then breaks his fast and eats.
His servants are surprised, since David was fasting when the child was still alive but not now, after he's died.
David replies, saying that he fasted because he thought there might be a chance God would spare the child.
But now there's no point—David will go to his child in death, but his child won't come back to him in life.

David consoles Bathsheba, and they have another child—Solomon (who will grow up to succeed David as king).
God loves Solomon and sends Nathan to convey this through a message. They give Solomon the second name Jedidiah, meaning "Beloved of the Lord."
Meanwhile, Joab keeps fighting the Ammonites, and takes their royal city. He tells David to come and lead the rest of the army to take over the rest of the city of Rabbah (not just the royal part, apparently), so that it will be called by David's name and not Joab's.
David succeeds, takes the king's crown, plunders the city, makes its citizens work at hard labor, and then proceeds to make short work of the other Ammonite cities.