Also, please notice that David's punishment was supposed to be his execution. In fact, unwittingly, David spelled out his own punishment. Please recall that Nathan, the prophet, tricked unrepentant David into facing his own sins by using an illustration of an anonymous rich man, who stole a poor man's only pet lamb:
The Holy Spirit by way of the prophets wrote:So David's anger was greatly aroused against the man, and he said to Nathan, "As the Lord lives, the man who has done this shall surely die!. And he shall restore fourfold for the lamb, because he did this thing and because he had no pity."
Then Nathan said to David, "You are the man! Thus says the Lord God of Israel ..."
After hearing his fate and the foretelling of all the awful, awaiting consequences to his sin - on top of his death - David repented:
So David said to Nathan, "I have sinned against the Lord." And Nathan said to David "The Lord also has put away your sin; you shall not die." (II Samuel 12:1-15)
As was said in the previous post, outside of God, there were not enough witnesses to justify David's execution according to Jewish Law. This is why the Jews could not have executed him, permorming "capital punishment". However, God saw the crime and had senteneced David to death, using David's own judgment. Yet, when David repented, God granted some clemency in sparing David's life, even though death may have been preferred, had David been allowed it as an alternative to the devestation his family suffered as a consequence of his sins.
Back to point, the lack of witnesses and
God's clemency and mercy are the reasons why David did not suffer execution by the hand of the civil authorities or God's direct judgment.
As you mentioned in the beginning, God has clearly authorized captial punishment in both the Old and New Covenants. Now, as ultimate Lawgiver and Judge, who bestows authority to the civil governments, He has the right grant clemency and mercy as He sees fit. That is His right.
I think the important lesson, whether one is pondering capital punishment or eternal judgment, we must realize that God has demonstrated the ability and possability of granting clemency beyond what He has promised. However, we have no promise, revelation, or basis for acting upon such. In other words, whether I am looking at the thief on the cross, or David's sin with Baathsheba, I cannot presume
that God will spare me in a similar way - above and beyond what He has promised.
The sin of presumption, when discussed in the Bible, is almost always connected with an immediate, capital punishment. Such people typically forfeited thier lives for presuming upon God (Nadab and Abihu, Korah and Dathan, Israelites taking land after bad report, Uzzah, Saul, etc...). Presumption is one of the most dangerous sins one can commit - both physically and spiritually.
Don't forget, people like David and Paul are exceptions
to God's rule. People like Uzzah, Nadab and Abihu, et al
, these are the rule
. The consequences of sin are death (Romans 6:23
). God could justly take the life of all men, immediately following sin as punishment of their sin. However, after each one of us sin, He grants clemency to all. Every time we draw breath, we do so in mercy. Our existence, like David and Paul, are the exceptions. Uzzah, Annanias and Sapphira, and the others, demonstrate the rule. The continued existence of every sinner continue to demonstrate God's mercy and clemency - at least for now... Of course, there is coming a day, when the time for mercy will be over and eternal judgment will be meeted out (Acts 17:30-31