Despised the word of the Lord is have sin

2 Samuel 12:1-15
The Lord sent Nathan to David. He rebuked David. Why have you despised the word of the Lord, to do what is evil in his sight? You have struck down Uriah the Hittite with the sword and have taken the his wife to be your wife and have killed him with the sword of the Ammonites.
The penalty from the Lord are
1)The sword shall never depart from your house.
2)Raise up evil against you out of your own house.
3)Take your wives before your eyes and give them to your neighbor, and he shall lie with your wives in the sight of this sun.
4)The child who is born to you shall die.
Davie committed his sin when Nathan revealed his sin, so he shall no die.
Uriah is dead; the wedding over; the child born. It all seems to have blown over very nicely - until Nathan arrives.
And then, by means of a simple little story with a sting in its tail, the whole sordid 污穢 episode is exposed.
The prophet's tale slips under David's guard, in the way of stories, and suddenly David sees himself as God sees him: a humbling experience for a king. God forgives him, but he is punished.
Why?
Pay four times over: Exodus 22:1 If a man steaks an ox or a sheep, and kills it or sells it, he shall repay five oxen for an ox, and four sheep for a sheep.
David is humble and confess his sin so he shall not die, but the punishment is remain and he has to suffer it.
How?
One have to pay cost for his sin then his sin may be erased.