Ok here's my thoughts as limited as they may seem and I'm open to corrections as always.
Forgive me if my post is a bit clunky.
My understanding is that Law was given to ancient Israel who were a theocracy.
Surely if the Law of God is given by God then it must be perfect.
The law of God was given to Israel as a standard he expected keep to set them apart from the rest of the world around them. To reveal the perfect standard of God and his holiness. They were about to enter into a land that in the eyes of God was so corrupt particularly with sexual licentiousness.
A land that was promised long before they entered it (side note I'm sure I read that God said they could not enter it until the sins of the inhabitants had gone so far that they could/would not repent of that but I can't find it at this moment)
Why some sin under the old Covent was punishable by death and some not I don't know.
We know that when Adam and Eve sinned then death entered to world.
Adam and Eve were created for each other, joining of the flesh. One man one woman. To me it seems obvious that God took sexual sin-adultery very seriously along with other sins like murder, idolatry.
Under the Old Covenant both parities involved in adultery were to be put to death.
What I find interesting about the adulteress woman bought before Jesus it was only her, what about the man?
A trap me thinks, one that Jesus doesn't fall into. "Let he who has not sinned cast the first stone"
Wow what a statement.
The wages of sin is death. And that is not limited to what I've mentioned above.
So I do not think in the New Covenant were are under the theocracy of Israel. Jesus is the High Priest that governs his new Church after his death.
Jesus when he walked the earth came to reveal the true heart of the Father. He didn't come to do away the law but to fulfil it. He knew we could not keep it. We can't keep to Holy standard of the father. He did.
The wages of sin is death, capital punishment.
Jesus took that capital punishment on the cross.
He died for every sin that mankind will do on the cross. All of our sins were placed on him, including adultery and other sins under the Old Covenant that required death.
Price paid, punishment exacted, sins forgiven when we accept his death for us.
For those who don't accept it their sins are still forgiven, price still paid. That is the Gospel, it's down to us to tell them and up to them to accept it.
My limited thoughts