God slowly killed David's baby boy to punish David for adultery

You've probably heard the story about David and Bathsheba. You know, the one where David sees Bathsheba taking a bath, and since he likes what he sees, he has sex with her. 

In an eveningtide, that David arose from off his bed, and walked upon the roof of the king's house: and from the roof he saw a woman washing herself; and the woman was very beautiful to look upon. And David sent and enquired after the woman. And one said, Is not this Bathsheba, the daughter of Eliam, the wife of Uriah the Hittite? And David sent messengers, and took her; and she came in unto him, and he lay with her. 2 Samuel 11.2-4

She becomes pregnant with David's child and David sends her husband (Uriah) into the front lines to be killed. 

The woman conceived, and sent and told David, and said, I am with child. 11.5

In the morning … David wrote a letter to Joab, and sent it by the hand of Uriah … saying, Set ye Uriah in the forefront of the hottest battle, and retire ye from him, that he may be smitten, and die … And Uriah the Hittite died. 11.14-17

Well, that's not what this story is about. In fact, the killing of Uriah is the only one of David's many killings that God disapproved of. David had Uriah killed and God had nothing to do with it. 

The thing that David had done displeased the LORD. 11.27

God was displeased with David for killing Uriah and taking his wife, but he forgave him for it. 

The LORD also hath put away thy sin; thou shalt not die. 12.13

Still, God had to do something to show his displeasure. Here's what he decided to do: he'd have David's wives raped by his neighbor while everyone else watches. 

Thus saith the LORD, Behold, I will raise up evil against thee out of thine own house, and I will take thy wives before thine eyes, and give them unto thy neighbour, and he shall lie with thy wives in the sight of this sun. 12.11

It turns out that the "neighbor" that God sends to do his dirty work is David's own son, Absalom. 

Ahithophel said unto Absalom, Go in unto thy father's concubines, which he hath left to keep the house … So they spread Absalom a tent upon the top of the house; and Absalom went in unto his father's concubines in the sight of all Israel. 2 Samuel 16.21-22

But that didn't quite do it. David had caused God's enemies to blaspheme, so God had to give them something else to blaspheme about. But what? 

Kill the baby, that's what. 

Because by this deed thou hast given great occasion to the enemies of the LORD to blaspheme, the child also that is born unto thee shall surely die. 12.14

And that's what God did, but not all at once. He let the baby suffer for a while. 

The LORD struck the child that Uriah's wife bare unto David, and it was very sick. 12.15

When God made the baby sick, David pleaded with God to stop tormenting him. But God wouldn't listen. 

David therefore besought God for the child; and David fasted, and went in, and lay all night upon the earth. 12.16

Finally, after the baby suffered for seven days, God killed him. 

On the seventh day, that the child died. 12.18

After the baby died, David washed, got dressed, had a nice meal, and worshiped the God who killed his son. 

David arose from the earth, and washed, and anointed himself, and changed his apparel, and came into the house of the LORD, and worshipped: then he ... did eat. 12.20

The story has a happy ending, though. After Bathsheba's baby boy is killed by God, David comforts her by going "in unto her." (He's such a nice guy!) 

David comforted Bathsheba his wife, and went in unto her. 12.24a

And Bathsheba conceives and bears another son (Solomon). 

And she bare a son, and he called his name Solomon. 12.24b

And God loved Solomon. 

And the LORD loved him. 12.24c

(He probably said to himself, as the Brick Testament suggests, “I don’t think I’ll kill this one.”)