Chapters 19-21 deal w/ various sins and punishments. Largely it’s all about “be holy for I am holy.” Also, don’t be like the pagans – they practiced a lot of things kin to idolatry. Don’t be like them.
However, there’s several sins in chapter 20 that result in death of the person committing them. Why?
Why do these sins results in death where others might have a sacrifice? Are they just “so bad” that you have to die? Is it indicative of the type of person (not just an act, but how they are)? Or maybe the defilement of these sins need to be eradicated???
I believe it’s the last one – that these sins can’t be just removed. Their effects are lasting. If you sacrifice your child, that will always be there. If you commit incest, that remains. Killing the person that commits it doesn’t make it go away, but it removes the cause in that sense.