Hi Anna @AnnaLinzey: Pastor Jim @jlyons has done a wonderful job of explaining and answering your question. I’d like to add a couple of thoughts.
As Pastor Jim indicated, we don’t see in the OT all that was followed through when it came to Law. Those that are recorded, 1Cor.10:11 says were done so to be a warning and example to us today…not that we will necessarily die, but that we won’t commit the same disobedient behavior the Israelites did. It think that was the purpose of the many laws requiring the death penalty. It was not so much punishment as it was meant to be a deterrent.
When it came to sins committed by individuals who were not killed for their crimes, such as David, what we also may not see recorded are the sin sacrifices they were to bring to the priests to offer on the altar. So, while there may have been private prayers of repentance, they also needed to offer sin sacrifices.
Another example of God not allowing one to be killed after he committed murder is Cain, the first murderer. God protected him from being slain.(Gen.4:14-15) This was prior to the Law, of course. However, God told Noah, prior to the Law, that anyone who killed the image of God, was to be killed. (Gen.9:6).
When the Israelites made the golden calf while Moses was receiving the commandments, God was so angry He wanted to wipe them all out, but only killed 3000. Because of Moses’ intercession, He later punished the rest with a plague. (Ex. 32)
In the New Testament, the woman caught in adultery was brought to Jesus for judgment. She, by law, was to be stoned. Yet, Jesus spared her life because He knew the evil intent of her accusers. It was not to pass judgment on her, but on Jesus. (John 8:1-11)
The Apostle Paul certainly was worthy of death for all the murder of the saints and followers of Christ he had ordered. Yet, Paul wrote the bulk of the New Testament.
Interestingly, in Matthew 5:38, Jesus left out “life for life” when He quoted Exodus 21:23-24 that also includes tooth for tooth, eye for eye, etc… So, the question can be asked if Jesus abolished the death penalty through His death on the cross, or is it still valid because it is taking the image of God?
In our times, on February, 3,1998, the first woman was executed in Texas for her crime of drug-induced mass murder. During her incarceration, she accepted Christ and became a model of a beautiful, transformed life. While she pleaded for the state to have mercy, she also humbled herself to the will of the state.
Tom Terrants was a former KKK member who should be dead today after a shoot-out with police that left him riddled with bullets. He had been instrumental in killing many during his years with the KKK. Yet, he lives today and was the former Director of the C.S.Lewis Institute, stepping down to further the call of God on his life. Why was he allowed to live?
I think the answer lies in Romans 9:14 which repeats what God told Moses in Ex.33:19 when He caused His Presence to pass before Moses:
"I will have mercy on whom I will have mercy and I will have compassion on whom I will have compassion."
Because God looks on the heart, as He knew David’s, it may also be that His mercy extends to others who violate(d) His Law. It is also that His purposes might be fulfilled, as Romans 9:11 indicates. So, there are various reasons why we read of some being killed for their sins and some not in the Old Testament on through to today. Ultimately, it is the mercy and purposes of God that decide.